isomers of C5H9F , C5H9Cl , C5H9Br and C5H9I

Advanced level organic chemistry PART 14.7: Constitutional isomers of molecular formula C5H9X (X = halogen)

Doc Brown's Advanced Chemistry: Part 14.7

Structural isomers and stereoisomers of molecular formula C5H9F, C5H9Cl, C5H9Br or C5H9I

[Author ©  Dr WP Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK advanced level chemistry courses, IB advanced chemistry & US K12 grades 11-12 and AP honors chemistry courses: Molecular spectroscopy and analysing the isomers of C5H9X [updated Feb 23rd 2026 *]

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35 selected constitutional-structural isomers of molecular formula C5H9X (X = halogen)

Introduction to constitutional-structural isomers and stereoisomers of molecular formula C5H9X (X = halogen)

35 constituent isomers of C5H9Cl, C5H9Br, C5H9I or C5H9F, names, skeletal formula types of isomerism how to analysise C5H9Cl C5H9Br C5H9I C5H9F for alkenes cycloalkanes E/Z geometrical isomers, R/S optical positional isomers of C5H9Cl C5H9Br C5H9I C5H9F

Relative molecular mass and percent composition of C5H9X (X = halogen) based on atomic masses:

C 12.01,  H 1.01, F 19.00,  Cl 35.45,  Br 79.90, I 126.90
Formula of compound Relative molecular mass % carbon % hydrogen % halogen
C5H9F 88.14 68.13 10.31 21.56
C5H9Cl 104.59 57.42 8.69 33.89
C5H9Br 149.04 40.29 6.10 53.61
C5H9I 196.04 30.63 4.64 64.73

Empirical formula = molecular formula = C5H9X (where X = a single halogen atom)

If applicable (see isomerism summary at the end of the page)

Structural isomerism  - isomers of the same specific molecular formula, based on different connectivity's of the constituent atoms (the constitutional isomers), so they cannot be spatially identical (but sometimes can be defined as having the same shape).

This includes (a) carbon chain variation (usually need a minimum of 4 atoms), (b) change in position of a substituent or functional group and (c) functional group isomerism where the atoms have a different connectivity configuration, usually with significant differences in chemical and physical properties e.g.

In terms of isomers of C5H9X there are

(a) chain variations based on the C atoms, open chain aliphatic linear, branched and cyclic (alicyclic) structures,

(b) positional isomers e.g. the -X halogen or alkene groups in all of these isomers,

(c) most are all functional group isomers of each other e.g. in terms of halogen substituted unsaturated alkenes or halogen substituted saturated cycloalkanes

Stereoisomerism - isomers based on the same connectivity of the atoms (same constitutional formula), but in some way, they are 2D or 3D spatially different non-superimposable images (e.g. E/Z 'geometrical' isomers or mirror image R/S 'optical' isomers)

This is where molecules have the same basic constitutional structural formula, but isomers differ in the 2D/3D arrangement of the atoms.

For stereoisomers, the (CIP) abbreviation means the IUPAC Cahn-Ingold-Prelog priority order rule for assigning E/Z (geometrical) and R/S (optical) stereoisomers.

E/Z stereoisomerism was called 'geometrical isomerism' e.g. cis (= Z) and trans (= E) isomers of alkenes or disubstituted cyclic alkanes where there are 2D/3D spatial variations that are not mirror images and not super imposable.

There are examples E/Z geometrical isomers in both the open chain compounds via the C=C restricted rotation or two substituents in the ring where both can be above the 'plane' of the ring or one above and one below the plane of the ring - can be complicated with overlapping R/S optical isomerism for the same molecule.

R/S stereoisomerism was called 'optical isomerism', the pairs of isomers are called enantiomers which are 3D non-superimposable mirror image forms of the molecule (enantiomers). The molecule must have a chiral centre (a stereocentre), that is an asymmetric carbon atom with four different atoms/groups attached to it.

There are examples R/S optical isomers in both the open chain aliphatic compounds or in the ring alicyclic compounds, but can be complicated with overlapping E/Z geometric isomers for the same molecule.

NOTE

Some of the C5H9X (X = halogen) isomers described may be highly reactive and very thermodynamically unstable e.g. due to weak highly strained bonds and some may not even exist at all (except theoretically of course!).

I've identified 21 open chain aliphatic constitutional isomers and 14 constitutional cyclic isomers (alicyclic) constitutional isomers.

This gives a total of 35 constitutional isomers for C5H9X

At least 21 of the constitutional isomers give at least one pair of E/Z geometrical isomers OR a pair of R/S optical isomers (enantiomers).

So there at least 56 distinct isomers for each formula from C5H9F, C5H9Cl, C5H9Br or C5H9I

I have done by best to provide the preferred IUPAC name for these isomers.

Please let me know if you think there are other isomers?

Introduction and details of selected isomers in molecules of formulae C5H9F, C5H9Cl, C5H9Br and C5H9I

(1) E/Z geometrical isomers 1-fluoropent-1-ene, 1-chloropent-1-ene, 1-bromopent-1-ene, 1-iodopent-1-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a linear alkene (pent-1-ene derivative).

1-fluoropent-1-ene,  1-chloropent-1-ene,  1-bromopent-1-ene,  1-iodopent-1-ene

Exhibits E/Z geometrical isomerism via the 1-ene alkene double bond (C1=C2).

CIP assignment priority rule for E/Z isomers: ZX   >  6C1H  > 1H

CIP rule around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 2 : 1 : 1 (for equivalent protons)

 

(2) 2-fluoropent-1-ene, 2-chloropent-1-ene, 2-bromopent-1-ene, 2-iodopent-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a linear alkene (pent-1-ene derivative)

2-fluoropent-1-ene,  2-chloropent-1-ene,  2-bromopent-1-ene,  2-iodopent-1-ene

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 2 : 2 (for equivalent protons)

 

(3) R/S optical isomers 3-fluoropent-1-ene, 3-chloropent-1-ene, 3-bromopent-1-ene, 3-iodopent-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a linear alkene (pent-1-ene derivative)

3-fluoropent-1-ene,  3-chloropent-1-ene,  3-bromopent-1-ene,  3-iodopent-1-ene

Exhibits R/S optical isomerism, carbon atom C3 is asymmetric (chiral).

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 1 : 1 : 2 (for equivalent protons)

 

(4) R/S optical isomers 4-fluoropent-1-ene, 4-chloropent-1-ene, 4-bromopent-1-ene, 4-iodopent-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a linear alkene (pent-1-ene derivative)

4-fluoropent-1-ene,  4-chloropent-1-ene,  4-bromopent-1-ene,  4-iodopent-1-ene

Exhibits R/S optical isomerism, carbon atom C4 is asymmetric (chiral).

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 1 : 2 : 1 : 2 (for equivalent protons)

 

(5) 5-fluoropent-1-ene, 5-chloropent-1-ene, 5-bromopent-1-ene, 5-iodopent-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a linear alkene (pent-1-ene derivative)

5-fluoropent-1-ene,  5-chloropent-1-ene,  5-bromopent-1-ene,  5-iodopent-1-ene

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 2 : 2 : 1 : 2 (for equivalent protons)

 

(6) E/Z geometrical isomers 1-fluoropent-2-ene, 1-chloropent-2-ene, 1-bromopent-2-ene, 1-iodopent-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a linear alkene (pent-2-ene derivative)

1-fluoropent-2-ene,  1-chloropent-2-ene,  1-bromopent-2-ene,  1-iodopent-2-ene

Exhibits E/Z geometrical isomerism via the 2-ene alkene double bond C2=C3.

CIP assignment priority rule for E/Z isomers: 6C  >  1H

CIP rule for atoms/groups around the >C=C< double bond

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 1 : 1 : 2 (for equivalent protons)

 

(7) E/Z geometrical isomers 2-fluoropent-2-ene, 2-chloropent-2-ene, 2-bromopent-2-ene, 2-iodopent-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a linear alkene (pent-2-ene derivative)

2-fluoropent-2-ene,  2-chloropent-2-ene,  2-bromopent-2-ene,  2-iodopent-2-ene

Exhibits E/Z geometrical isomerism via the 2-ene alkene double bond C2=C3.

CIP assignment priority rule for E/Z isomers: ZX >  6C6C  >  6C1H > 1H

CIP rule for atoms/groups around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 1 : 3 (for equivalent protons)

 

(8) E/Z geometrical isomers 3-fluoropent-2-ene, 3-chloropent-2-ene, 3-bromopent-2-ene, 3-iodopent-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a linear alkene (pent-2-ene derivative)

3-fluoropent-2-ene,  3-chloropent-2-ene,  3-bromopent-2-ene,  3-iodopent-2-ene

Exhibits E/Z geometrical isomerism via the 2-ene alkene double bond C2=C3.

CIP assignment priority rule for E/Z isomers: ZX >  6C6C  >  6C1H > 1H

CIP rule for atoms/groups around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 1 : 3 (for equivalent protons)

 

(9) E/Z geometrical isomers 4-fluoropent-2-ene, 4-chloropent-2-ene, 4-bromopent-2-ene, 4-iodopent-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a linear alkene (pent-2-ene derivative)

4-fluoropent-2-ene,  4-chloropent-2-ene,  4-bromopent-2-ene,  4-iodopent-2-ene

Exhibits E/Z geometrical isomerism via the 2-ene alkene double bond .C2=C3.

CIP assignment priority rule for E/Z isomers: 6CZX or 6C6C  >  6C1H > 1H

CIP rule for atoms/groups around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 1 : 1 : 1 : 3 (for equivalent protons)

 

(10) E/Z geometrical isomers 5-fluoropent-2-ene, 5-chloropent-2-ene, 5-bromopent-2-ene, 5-iodopent-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a linear alkene (pent-2-ene derivative)

5-fluoropent-2-ene,  5-chloropent-2-ene,  5-bromopent-2-ene,  5-iodopent-2-ene

Exhibits E/Z geometrical isomerism via the 2-ene alkene double bond C2=C3.

CIP assignment priority rule for E/Z isomers: 6C > 1H

CIP rule for atoms/groups around the >C=C< double bond

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 2 : 1 : 1 : 3 (for equivalent protons)

 

(11) E/Z geometrical isomers 1-fluoro-2-methylbut-1-ene, 1-chloro-2-methylbut-1-ene, 1-bromo-2-methylbut-1-ene, 1-iodo-2-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a branched alkene (2-methylbut-1-ene derivative)

1-fluoro-2-methylbut-1-ene,  1-chloro-2-methylbut-1-ene,  1-bromo-2-methylbut-1-ene,  1-iodo-2-methylbut-1-ene

Exhibits E/Z geometrical isomerism via the 1-ene alkene double bond C2=C3.

CIP assignment priority rule for E/Z isomers: ZX  >   6C6C  >  6C1H > 1H

CIP rule for atoms/groups around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 3 : 1 (for equivalent protons)

 

(12) 2-(fluoromethyl)but-1-ene, 2-(chloromethyl)but-1-ene, 2-(bromomethyl)but-1-ene, 2-(iodomethyl)but-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (2-methylbut-1-ene derivative)

2-(fluoromethyl)but-1-ene,  2-(chloromethyl)but-1-ene,  2-(bromomethyl)but-1-ene,  2-(iodomethyl)but-1-ene

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 2 : 2 : 2 (for equivalent protons)

 

(13) R/S optical isomers 3-fluoro-2-methylbut-1-ene, 3-chloro-2-methylbut-1-ene, 3-bromo-2-methylbut-1-ene, 3-iodo-2-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (2-methylbut-1-ene derivative)

3-fluoro-2-methylbut-1-ene,  3-chloro-2-methylbut-1-ene,  3-bromo-2-methylbut-1-ene,  3-iodo-2-methylbut-1-ene

Exhibits R/S optical isomerism, carbon atom C3 is asymmetric (chiral).

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 1 : 3 : 2 (for equivalent protons)

 

(14) 4-fluoro-2-methylbut-1-ene, 4-chloro-2-methylbut-1-ene, 4-bromo-2-methylbut-1-ene, 4-iodo-2-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (2-methylbut-1-ene derivative)

4-fluoro-2-methylbut-1-ene,  4-chloro-2-methylbut-1-ene,  4-bromo-2-methylbut-1-ene,  4-iodo-2-methylbut-1-ene

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 2 : 3 : 2 (for equivalent protons)

 

(15) E/Z geometrical isomers 1-fluoro-3-methylbut-1-ene, 1-chloro-3-methylbut-1-ene, 1-bromo-3-methylbut-1-ene, 1-iodo-3-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a branched alkene (3-methylbut-1-ene derivative)

1-fluoro-3-methylbut-1-ene,  1-chloro-3-methylbut-1-ene,  1-bromo-3-methylbut-1-ene,  1-iodo-3-methylbut-1-ene

Exhibits E/Z geometrical isomerism via the 1-ene alkene double bond.

CIP assignment priority rule for E/Z isomers: ZX > 6C > 1H

CIP rule for atoms/groups around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 6 (3+3) : 1 : 1 : 1 (for equivalent protons)

 

(16) 2-fluoro-3-methylbut-1-ene, 2-chloro-3-methylbut-1-ene, 2-bromo-3-methylbut-1-ene, 2-iodo-3-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (3-methylbut-1-ene derivative)

2-fluoro-3-methylbut-1-ene,  2-chloro-3-methylbut-1-ene,  2-bromo-3-methylbut-1-ene,  2-iodo-3-methylbut-1-ene

Number of low resolution NMR chemical shift δ signal peaks: 3 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 6 (3+3) : 1 : 2 (for equivalent protons)

 

(17) 3-fluoro-3-methylbut-1-ene, 3-chloro-3-methylbut-1-ene, 3-bromo-3-methylbut-1-ene, 3-iodo-3-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (3-methylbut-1-ene derivative)

3-fluoro-3-methylbut-1-ene,  3-chloro-3-methylbut-1-ene,  3-bromo-3-methylbut-1-ene,  3-iodo-3-methylbut-1-ene

Number of low resolution NMR chemical shift δ signal peaks: 3 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 6 (3+3) : 1 : 2 (for equivalent protons)

 

(18) R/S optical isomers 4-fluoro-3-methylbut-1-ene, 4-chloro-3-methylbut-1-ene, 4-bromo-3-methylbut-1-ene, 4-iodo-3-methylbut-1-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (3-methylbut-1-ene derivative)

4-fluoro-3-methylbut-1-ene,  4-chloro-3-methylbut-1-ene,  4-bromo-3-methylbut-1-ene,  4-iodo-3-methylbut-1-ene

Exhibits R/S optical isomerism, carbon atom 3 is asymmetric (chiral).

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 1 : 3 : 1 : 2 (for equivalent protons)

 

(19) E/Z geometrical isomers 1-fluoro-2-methylbut-2-ene, 1-chloro-2-methylbut-2-ene, 1-bromo-2-methylbut-2-ene, 1-iodo-2-methylbut-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a branched alkene (2-methylbut-2-ene derivative)

1-fluoro-2-methylbut-2-ene,  1-chloro-2-methylbut-2-ene,  1-bromo-2-methylbut-2-ene,  1-iodo-2-methylbut-2-ene

Exhibits E/Z geometrical isomerism via the 2-ene alkene double bond.

CIP assignment priority rule for E/Z isomers: 6CZX  >  6C1H > 1H

CIP rule for atoms/groups around the >C=C< double bond, (X = halogen, Z = 9, 17, 35 or 53)

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 1 : 3 : 2 (for equivalent protons)

 

(20) 2-fluoro-3-methylbut-2-ene, 2-chloro-3-methylbut-2-ene, 2-bromo-3-methylbut-2-ene, 2-iodo-3-methylbut-2-ene skeletal formula constitutional structural formuka molecular formula Halogen substituted derivative of a branched alkene (2-methylbut-2-ene derivative)

2-fluoro-3-methylbut-2-ene,  2-chloro-3-methylbut-2-ene,  2-bromo-3-methylbut-2-ene,  2-iodo-3-methylbut-2-ene

Number of low resolution NMR chemical shift δ signal peaks: 3/4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 6 (3+3, might split?) (for equivalent protons)

 

(21) 1-fluoro-3-methylbut-2-ene, 1-chloro-3-methylbut-2-ene, 1-bromo-3-methylbut-2-ene, 1-iodo-3-methylbut-2-ene skeletal formula constitutional structural formuka molecular formula

Halogen substituted derivative of a branched alkene (2-methylbut-2-ene derivative)

1-fluoro-3-methylbut-2-ene,  1-chloro-3-methylbut-2-ene,  1-bromo-3-methylbut-2-ene,  1-iodo-3-methylbut-2-ene

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 1 : 6 (3+3, might split?) (for equivalent protons)

 

(22) fluorocyclopentane, chlorocyclopentane, bromocyclopentane, iodocyclopentane skeletal formula constitutional structural formuka molecular formula monosubstituted derivative of cyclobutane

fluorocyclopentane,  chlorocyclopentane,  bromocyclopentane,  iodocyclopentane

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 3 13C (email if disagree?)

1H NMR ratio of peaks: 4 (2+2) : 4 (2+2) : 1 (for equivalent protons)

 

(23) 1-fluoro-1-methylcyclobutane, 1-chloro-1-methylcyclobutane, 1-bromo-1-methylcyclobutane, 1-iodo-1-methylcyclobutane skeletal formula constitutional structural formuka molecular formula disubstituted derivative of cyclobutane

1-fluoro-1-methylcyclobutane,  1-chloro-1-methylcyclobutane,  1-bromo-1-methylcyclobutane,  1-iodo-1-methylcyclobutane

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 4 (2+2) : 2 (for equivalent protons)

 

(24) R/S optical E/Z geometrical isomers 1-fluoro-2-methylcyclobutane, 1-chloro-2-methylcyclobutane, 1-bromo-2-methylcyclobutane, 1-iodo-2-methylcyclobutane skeletal formula constitutional structural formuka molecular formula disubstituted derivative of cyclobutane

1-fluoro-2-methylcyclobutane,  1-chloro-2-methylcyclobutane,  1-bromo-2-methylcyclobutane,  1-iodo-2-methylcyclobutane

Exhibits R/S optical isomerism, ring carbon atoms C1 and C2 are asymmetric (chiral), but the two substituents in the cyclobutane ring give rise to overlapping E/Z geometrical isomerism - requires university level analysis.

Something of a contrast with (23) in terms of isomerism!

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 1 : 2 : 2 : 1 (for equivalent protons)

 

(25) E/Z geometrical isomers 1-fluoro-3-methylcyclobutane, 1-chloro-3-methylcyclobutane, 1-bromo-3-methylcyclobutane, 1-iodo-3-methylcyclobutane skeletal formula constitutional structural formuka molecular formula and R/S isomers, disubstituted derivative of cyclobutane

1-fluoro-3-methylcyclobutane,  1-chloro-3-methylcyclobutane,  1-bromo-3-methylcyclobutane,  1-iodo-3-methylcyclobutane

Exhibits E/Z geometrical isomerism via the two substituents in the cyclobutane ring and R/S optical isomerism. Complex stereoisomerism, two chiral centres (ring C1 and C3), needs university level analysis.

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 3 : 1 : 4 (2+2) : 1 (for equivalent protons)

 

(26) (fluoromethyl)cyclobutane, (chloromethyl)cyclobutane, (bromomethyl)cyclobutane, (iodomethyl)cyclobutane skeletal formula constitutional structural formuka molecular formula monosubstituted derivative of cyclobutane

(fluoromethyl)cyclobutane,  (chloromethyl)cyclobutane,  (bromomethyl)cyclobutane,  (iodomethyl)cyclobutane

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 1 : 4 (2+2) : 2 (for equivalent protons)

 

(27) 1-ethyl-1-fluorocyclopropane, 1-chloro-1-ethylcyclopropane, 1-bromo-1-ethylcyclopropane, 1-ethyl-1-iodocyclopropane skeletal fo2mula constitutional structural formuka molecular formula disubstituted cyclopropane derivative

1-ethyl-1-fluorocyclopropane,  1-chloro-1-ethylcyclopropane,  1-bromo-1-ethylcyclopropane, 1-ethyl-1-iodocyclopropane

Number of low resolution NMR chemical shift δ signal peaks: 3 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 4 (2+2) : 2 : 3 (for equivalent protons)

 

(28) R/S optical E/Z geometrical isomers 1-ethyl-2-fluorocyclopropane, 1-chloro-2-ethylcyclopropane, 1-bromo-2-ethylcyclopropane, 1-ethyl-2-iodocyclopropane skeletal formula constitutional structural formuka molecular formula disubstituted cyclopropane derivative

1-ethyl-2-fluorocyclopropane,  1-chloro-2-ethylcyclopropane,  1-bromo-2-ethylcyclopropane, 1-ethyl-2-iodocyclopropane

Exhibits E/Z geometrical isomerism via the two substituents in the cyclopropane ring, but the two ring carbons of the substituent groups are both asymmetric (chiral) so R/S optical isomerism overlaps with E/Z geometrical isomerism - complicated stereoisomerism, two chiral centres (ring C1 and C2), university level analysis required.

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 1 : 1 : 2 : 3 (for equivalent protons)

 

(29) R/S optical isomers (1-fluoroethyl)cyclopropane, (1-chloroethyl)cyclopropane, (1-bromoethyl)cyclopropane, (1-iodoethyl)cyclopropane skeletal formula constitutional structural formuka molecular formula monosubstituted cyclopropane derivative

(1-fluoroethyl)cyclopropane,  (1-chloroethyl)cyclopropane,  (1-bromoethyl)cyclopropane,  (1-iodoethyl)cyclopropane

Exhibits R/S optical isomerism, the C of the C-X bond is asymmetric (chiral).

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 4 (2+2) : 1 : 1 : 3 (for equivalent protons)

 

(30) (2-fluoroethyl)cyclopropane, (2-chloroethyl)cyclopropane, (2-bromoethyl)cyclopropane, (2-iodoethyl)cyclopropane skeletal formula constitutional structural formuka molecular formula monosubstituted cyclopropane derivative

(2-fluoroethyl)cyclopropane,  (2-chloroethyl)cyclopropane,  (2-bromoethyl)cyclopropane,  (2-iodoethyl)cyclopropane

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 4 (2+2) : 1 : 2 : 2 (for equivalent protons)

 

(31) 1-(fluoromethyl)-1-methylcyclopropane, 1-(chloromethyl)-1-methylcyclopropane, 1-(bromomethyl)-1-methylcyclopropane, 1-(iodomethyl)-1-methylcyclopropane skeletal formula constitutional structural formuka molecular formula disubstituted cyclopropane derivative

1-(fluoromethyl)-1-methylcyclopropane,  1-(chloromethyl)-1-methylcyclopropane,  1-(bromomethyl)-1-methylcyclopropane,  1-(iodomethyl)-1-methylcyclopropane

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 4 (2+2) : 3 : 2 (for equivalent protons)

 

(32) R/S optical E/Z geometrical isomers 1-(fluoromethyl)-2-methylcyclopropane, 1-(chloromethyl)-2-methylcyclopropane, 1-(bromomethyl)-2-methylcyclopropane, 1-(iodomethyl)-2-methylcyclopropane skeletal formula constitutional structural formuka molecular formula disubstituted cyclopropane derivative

1-(fluoromethyl)-2-methylcyclopropane,  1-(chloromethyl)-2-methylcyclopropane,  1-(bromomethyl)-2-methylcyclopropane,  1-(iodomethyl)-2-methylcyclopropane

Exhibits E/Z geometrical isomerism via the two substituents in the cyclopropane ring, but the two ring carbon (C1 and C2) are both asymmetric (chiral) so R/S optical isomerism overlaps with E/Z geometrical isomerism - complicated, university level analysis required.

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 1 : 3 : 1 : 2 (for equivalent protons)

 

(33) R/S optical isomers 1-fluoro-2,2-dimethylcyclopropane, 1-chloro-2,2-dimethylcyclopropane, 1-bromo-2,2-dimethylcyclopropane, 1-iodo-2,2-dimethylcyclopropane skeletal formula constitutional structural formuka molecular formula trisubstituted cyclopropane derivative

1-fluoro-2,2-dimethylcyclopropane,  1-chloro-2,2-dimethylcyclopropane,  1-bromo-2,2-dimethylcyclopropane,  1-iodo-2,2-dimethylcyclopropane

Exhibits R/S optical isomerism, the ring C1 of the C-X bond is asymmetric (chiral).

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 6 (3+3) : 1 (for equivalent protons)

 

(34) R/S optical E/Z geometrical isomers 1-fluoro-1,2-dimethylcyclopropane, 1-chloro-1,2-dimethylcyclopropane, 1-bromo-1,2-dimethylcyclopropane, 1-iodo-1,2-dimethylcyclopropane skeletal formula constitutional structural formuka molecular formula trisubstituted cyclopropane derivative

1-fluoro-1,2-dimethylcyclopropane,  1-chloro-1,2-dimethylcyclopropane,  1-bromo-1,2-dimethylcyclopropane,  1-iodo-1,2-dimethylcyclopropane

Exhibits E/Z geometrical isomerism via the three substituents in the cyclopropane ring, but the two ring carbons (C1 and C2) are both asymmetric (chiral) so R/S optical isomerism overlaps with E/Z geometrical isomerism - complicated, university level analysis required.

Number of low resolution NMR chemical shift δ signal peaks: 5 1H and 5 13C (email if disagree?)

1H NMR ratio of peaks: 2 : 3 : 1 : 3 (for equivalent protons)

 

(35) R/S optical E/Z geometrical isomers 1-fluoro-2,3-dimethylcyclopropane, 1-chloro-2,3-dimethylcyclopropane, 1-bromo-2,3-dimethylcyclopropane, 1-iodo-2,3-dimethylcyclopropane skeletal formula constitutional structural formuka molecular formula trisubstituted cyclopropane derivative

1-fluoro-2,3-dimethylcyclopropane,  1-chloro-2,3-dimethylcyclopropane,  1-bromo-2,3-dimethylcyclopropane,  1-iodo-2,3-dimethylcyclopropane

Exhibits E/Z geometrical isomerism via the three substituents in the cyclopropane ring, but the three ring carbon atoms are all asymmetric (chiral) so R/S optical isomerism overlaps with E/Z geometrical isomerism - complicated, university level analysis required.

Number of low resolution NMR chemical shift δ signal peaks: 4 1H and 4 13C (email if disagree?)

1H NMR ratio of peaks: 1 : 6 (3+3) : 2 (1+1) (for equivalent protons)

https://www.molport.com/shop/molecular-formula/C5H9Br shows 37 isomers of C5H9Br are commercially available

Summary of the isomers of molecular formula C5H9X (where X = F, Cl, Br or I)

The molecular formula C5H9X has a total of 35 constitutional isomers.

1. Constitutional isomers, also known as structural isomers, are molecules that share the same molecular formula but have different connectivity of atoms.

2 The number of possible isomers for C5H9X can be determined by systematically considering all possible arrangements of its carbon skeleton, the location of a double bond or ring, and the position of the chlorine atom.

3. The formula C5H9X has a degree of unsaturation of one, which indicates the presence of either one double bond or one ring structure in its isomers.

Breakdown of Isomers

There are two main categories of constitutional isomers for this formula:

Extra notes on physical and chemical properties of C5H9X compounds and selected uses

Isomers of C5H9X (X = F, Cl, Br, I) differ in boiling point, reactivity, and industrial use due to halogen identity and molecular structure. For example, 5-bromo-1-pentene is used in pharmaceutical synthesis, while chlorocyclopentane serves as a solvent and intermediate in agrochemicals.

Physical and Chemical Property Differences by Halogen

Halogen

Boiling Point

Density

Bond Strength (C–X)

Leaving Group Ability

Reactivity

F

Lowest (~60–70 °C)

~0.9 g/cm³

Strongest

Poor

Low (inert to SN reactions)

Cl

Moderate (~100–110 °C)

~1.0 g/cm³

Strong

Moderate

Moderate (SN1/SN2)

Br

Higher (~125–135 °C)

~1.25 g/cm³

Weaker

Good

High (SN1/SN2, radical)

I

Highest (~140–150 °C)

~1.5 g/cm³

Weakest

Excellent

Very high (SN1, coupling)

  • Boiling point and density increase down the group due to molar mass and polarizability.

  • Reactivity increases from F to I due to decreasing C–X bond strength and better leaving group ability.

  • Fluoroalkenes are less reactive but more stable; iodoalkenes are highly reactive but less stable.

Specific Isomers and Their Uses

5-Bromo-1-pentene

  • Properties: Boiling point ~126 °C; density ~1.26 g/cm³; reactive allylic bromide.

  • Reactivity: Undergoes SN2 and radical reactions; useful in polymer and pharmaceutical synthesis.

  • Applications:

    • Intermediate in drug synthesis and specialty polymers.

    • Used in radical bromination and Grignard reactions.

  • Safety: Flammable; irritant; requires cold storage.

Chlorocyclopentane

  • Structure: Cyclopentane ring with one Cl substituent.

  • Properties: Boiling point ~104 °C; density ~0.98 g/cm³; moderate volatility.

  • Reactivity: Undergoes SN1/SN2; stable under ambient conditions.

  • Applications:

    • Used as solvent and intermediate in agrochemical and pharmaceutical manufacturing.

    • Precursor in halogenated cyclic compounds.

5-Fluoro-1-pentene

  • Properties: Boiling point ~60–70 °C; low density; inert C–F bond.

  • Reactivity: Poor leaving group; limited SN reactions; stable under heat.

  • Applications:

    • Used in fluorinated polymers, PET tracers, and specialty agrochemicals.

    • Valuable for metabolic stability in drug design.

5-Iodo-1-pentene

  • Properties: Boiling point ~140 °C; high density; excellent leaving group.

  • Reactivity: Highly reactive in SN1, SN2, and cross-coupling reactions.

  • Applications:

    • Used in radioiodination, Suzuki coupling, and late-stage functionalisation in medicinal chemistry.

    • Valuable in labelled compounds for diagnostics.

Misconceptions to Avoid

  • “All halides react the same”: Reactivity varies greatly with halogen and position.

  • “Fluorides are most reactive”: C–F bonds are strongest and least reactive.

  • “Position doesn’t matter”: Allylic/vinylic halides behave differently from primary/secondary alkyl halides.

Exam Tips

  • Compare SN1 versus SN2: Use halogen identity and carbon type (primary, secondary, tertiary).

  • Use boiling point trends: Heavier halogens = higher bp.

  • Link structure to use: Allylic halides = reactive intermediates; cyclic halides = solvents or precursors.

  • Practice naming and drawing: Isomers like 5-bromo-1-pentene versus 1-bromo-2-pentene differ in reactivity and application.

A summary chart of isomerism

index for all isomerism pages

Associated organic chemistry  links

Index of sets of isomers for a given molecular formula

Isomerism: introduction, structural isomerism - chain, positional, functional group, tautomerism

Stereoisomerism: introduction, definition, priority rules, E/Z isomerism (cis/trans isomerism)

Stereoisomerism - R/S isomerism (optical isomerism) - definition - examples explained

Index of all IR, mass, 1H NMR and 13C NMR spectroscopy pages

This is a big chemistry website, please allow time to explore

Index of advanced (pre-university) organic chemistry revision notes

 The chemistry of alkanes and the petrochemical industry

 The chemistry of alkenes

 The chemistry of organic halogen compounds

 The chemistry of alcohols

The chemistry of aldehydes and ketones

 The chemistry of carboxylic acids and derivatives

The chemistry of organo-nitrogen compounds

The chemistry of aromatic compounds

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on isomerism are suitable for use of pre-university students studying AQA advanced level chemistry constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I, Edexcel advanced level chemistry constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I, OCR advanced level chemistry constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I, IB advanced level chemistry constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I, WJEC (Eduqas) advanced level chemistry constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I, CIE Cambridge advanced level chemistry constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I, US grade 11-12 AP honors chemistry courses  constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I and they will also prove useful to 1st year undergraduate students of chemistry including  constitutional isomers of C5H9F, C5H9Cl, C5H9Br and C5H9I.

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Are there any functional group isomers with a molecular formula C5H9Cl C5H9Br C5H9I C5H9F? Do C5H9Cl C5H9Br C5H9I C5H9F organic halogen molecules have any stereoisomers? Are there any E/Z (geometrical) isomers with a molecular formula C5H9Cl C5H9Br C5H9I C5H9F? Are there any R/S (optical) isomers (enantiomers) with a molecular formula C5H9Cl C5H9Br C5H9I C5H9F? Be able to deduce the isomers of organic halogen molecules with the formula C5H9Cl C5H9Br C5H9I C5H9F. Be able to draw and name the substituted halogen compounds isomers of molecular formula C5H9Cl C5H9Br C5H9I C5H9F. Be able to deduce if the isomers of C5H9Cl C5H9Br C5H9I C5H9F organic halogen compounds can exhibit R/S optical isomerism. Be able to deduce if the isomers of C5H9Cl C5H9Br C5H9I C5H9F can exhibit E/Z geometrical isomerism (do C5H9Cl C5H9Br C5H9I C5H9F have cis/trans geometric isomers). Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. Website content © Dr Phil Brown 2000+. All copyrights reserved on these organic chemistry exam revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, these A level chemistry revision notes are suitable for use of pre-university students studying AQA advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, Edexcel advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, OCR advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, IB advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, WJEC (Eduqas) advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, CIE Cambridge advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, CCEA advanced level organic chemistry revision notes on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, and useful for US grade 11 grade 12 AP honors organic chemistry courses involving  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F Explaining the importance of  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F in organic chemistry, What you need to know about  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F for organic chemistry, Explaining the use of  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F knowledge in organic chemistry, Examples of  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F explained when studying organic chemistry, What is the significance of  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F in organic chemistry, What is the use of  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F in organic chemistry  Describing and explaining the theory of  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F when studying organic chemistry, exam revision notes for  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F in exams, online help for  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, revision notes for  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, what do I need to learn for  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F in exams? revision summary for  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, help in teaching  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, learning notes for  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F, help to pass the  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F exam, how to prepare for examination questions on  isomers of C5H9Cl, C5H9Br, C5H9I & C5H9F?

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