(1-7) Alkynes - open chain aliphatic compounds with a carbon-carbon triple bond C≡C functional group.

(1) hex-1-yne, CH₃CH₂CH₂CH₂C≡CH , 1-hexyne, abbreviated structural formula

skeletal formula of a 'doubly' unsaturated alkyne.

Terms that be used to describe unsaturation:

Index of hydrogen deficiency (IHD) = 4, four H atoms can be added to the C≡C bond.

Double bond equivalents (DBE) = 2, two C=C bonds in the molecule.

Degree of unsaturation = 2, two C=C bonds in the molecule.

No E/Z or R/S isomerism possible for hex-1-yne.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 2 : 2 : 1 (for equivalent protons of the principal chemical shifts)

Index of ¹H NMR spectra organic compounds and Index of ¹³C NMR spectra organic compounds

 

(2) hex-2-yne, CH₃CH₂CH₂C≡CCH₃ , 2-hexyne, abbreviated structural formula

skeletal formula of this alkyne

No E/Z or R/S isomerism possible.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 2 : 3 (for equivalent protons of the principal chemical shifts)

 

(3) hex-3-yne, CH₃CH₂C≡CCH₂CH₃ , 3-hexyne, abbreviated structural formula

skeletal formula of this alkyne

No E/Z or R/S isomerism possible.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 6 (3+3) : 4 (2+2) (for equivalent protons of the principal chemical shifts)

Reduced number of peaks due to the symmetry of the molecule.

 

(4) 3-methylpent-1-yne, CH₃CH₂CH(CH₃)C≡CH , 3-methyl-1-pentyne, abbreviated structural formula

skeletal formula, R/S isomers possible of this alkyne, carbon atom 3 is chiral.

(R)-3-methylpent-1-yne, (S)-3-methylpent-1-yne, (R)-3-methyl-1-pentyne, (S)-3-methyl-1-pentyne

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 1 : 3 : 1 (for equivalent protons of the principal chemical shifts)

 

(5) 4-methylpent-1-yne, (CH₃)₂CHCH₂C≡CH , 4-methyl-1-pentyne, abbreviated structural formula

skeletal formula, No E/Z or R/S isomerism possible for this alkyne.

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

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

 

(6) 4-methylpent-2-yne, (CH₃)₂CHC≡CCH₃ , 4-methyl-2-pentyne, abbreviated structural formula

skeletal formula, No E/Z or R/S isomerism possible for this alkyne.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 6 (3+3) : 1 : 3 (for equivalent protons of the principal chemical shifts)

 

(7) 3,3-dimethylbut-1-yne, (CH₃)₃CC≡CH , 3,3-dimethyl-1-butyne

skeletal formula, No E/Z or R/S isomerism possible.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 9 (3x3) : 1 (for equivalent protons of the principal chemical shifts)

 

(8-22) Dienes - carbon chain and positional isomers

(8) hexa-1,2-diene, CH₃CH₂CH₂CH=C=CH₂ , 1,2-hexadiene, abbreviated structural formula

skeletal formula, No E/Z or R/S isomerism possible for this diene.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 2 : 1 : 2 (for equivalent protons of the principal chemical shifts)

 

(9) hexa-1,3-diene, CH₃CH₂CH=CHCH=CH₂ , 1,3-hexadiene, abbreviated structural formula

skeletal formula

E/Z isomers based on carbon atoms >C=C< 3 and 4, E (trans) and Z (cis) isomer shown here.

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

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

Other names: (E)-hexa-1,3-diene, (Z)-hexa-1,3-diene, (E)-1,3-hexadiene, (Z)-1,3-hexadiene, (3E)-hexa-1,3-diene, (3Z)-hexa-1,3-diene, (3E)-1,3-hexadiene, (3Z)-1,3-hexadiene

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 1 : 1 : 1 : 2 (for equivalent protons of the principal chemical shifts)

 

(10) hexa-1,4-diene, CH₃CH=CHCH₂CH=CH₂ , 1,4-hexadiene, abbreviated structural formula

skeletal formula

E/Z isomers based on carbon atoms 4 and 5, E (trans) and Z (cis) isomers shown here.

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

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

Other names: (E)-hexa-1,4-diene, (Z)-hexa-1,4-diene, (E)-1,4-hexadiene, (Z)-1,4-hexadiene, (4E)-hexa-1,4-diene, (4Z)-hexa-1,4-diene, (4E)-1,4-hexadiene, (4Z)-1,4-hexadiene

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 1 : 1 : 2 : 1 : 2 (for equivalent protons of the principal chemical shifts)

 

(11) hexa-1,5-diene, H₂C=CHCH₂CH₂CH=CH₂  , 1,5-hexadiene, abbreviated structural formula

skeletal formula, No E/Z or R/S isomerism possible.

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

¹H NMR ratio of peaks: 4 (2+2) : 2 (1+1) : 4 (2+2) (for equivalent protons of the principal chemical shifts). Reduced number of NMR peaks due to the symmetry of this diene molecule.

 

(12) hexa-2,3-diene, CH₃CH₂CH=C=CHCH₃, 2,3-hexadiene, abbreviated structural formula

skeletal formula,

This exhibits R/S (optical) isomerism because the pi orbitals of the adjacent C=C bonds are at 90^o to each other and allows the formation of non-superimposable mirror image forms (a bit subtle at pre-university, but make the models yourself!). The R/S isomers (pair of enantiomers) are best appreciated using ball and stick models (university level analysis).

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 1 : 1 : 3 (for equivalent protons of the principal chemical shifts)

 

(13) hexa-2,4-diene, CH₃CH=CHCH=CHCH₃, 2,4-hexadiene, abbreviated structural formula

skeletal formula, symmetrical alkene

E/Z isomers based on carbon atoms 2 and 3, three possible E/Z isomers.

CIP assignment priority rule for E/Z isomers: ₆C₆C  >  ₆C₁H  >  ₁H (a bit tricky!)

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

(E,E)-hexa-2,4-diene, (E,Z)-hexa-2,4-diene, (Z,Z)-hexa-2,4-diene, (E,E)-2,4-hexadiene, (E,Z)-2,4-hexadiene, (Z,Z)-2,4-hexadiene

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

¹H NMR ratio of peaks: 6 (3+3) : 2 (1+1) : 2 (1+1) (for equivalent protons, ignoring E/Z isomers)

 

(14) 3-methylpenta-1,2-diene, CH₃CH₂C(CH₃)=C=CH₂ , 3-methyl-1,2-pentadiene, abbreviated structural formula

skeletal formula, no E/Z or R/S isomerism possible for this diene.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 3 : 2 (for equivalent protons of the principal chemical shifts)

 

(15) 4-methylpenta-1,2-diene, (CH₃)₂CHCH=C=CH₂ , 4-methyl-1,2-pentadiene, abbreviated structural formula

skeletal formula, No E/Z or R/S isomerism possible.

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

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

 

(16) 2-methylpenta-1,3-diene, CH₃CH=CHC(CH₃)=CH₂ , 2-methyl-1,3-pentadiene, abbreviated structural formula

skeletal formula, E/Z stereoisomers (cis and trans) for this diene

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

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

(E)-2-methylpenta-1,4-diene, (Z)-2-methylpenta-1,4-diene, (E)-2-methyl-1,3-pentadiene, (Z)-2-methyl-1,3-pentadiene

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(17) 3-methylpenta-1,3-diene, CH₃CH=C(CH₃)CH=CH₂ , 3-methyl-1,3-pentadiene, abbreviated structural formula

skeletal formula, E/Z isomerism possible.

Other names: (E)-3-methylpenta-1,3-diene, (Z)-3-methylpenta-1,3-diene, (E)-3-methyl-1,3-pentadiene, (Z)-3-methyl-1,3-pentadiene

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

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

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 1 : 3 : 1 : 2 (for equivalent protons of the principal chemical shifts)

 

(18) 4-methylpenta-1,3-diene, (CH₃)₂C=CHCH=CH₂ , 4-methyl-1,3-pentadiene, abbreviated structural formula

skeletal formula, No E/Z and R/S isomers possible.

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

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

 

(19) 2-methylpenta-1,4-diene, H₂C=CHCH₂C(CH₃)=CH₂ , 2-methyl-1,4-pentadiene, abbreviated structural formula

skeletal formula, no E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 1 : 2 : 3 : 2 (for equivalent protons of the principal chemical shifts)

 

(20) 3-methylpenta-1,4-diene, H₂C=CHCH(CH₃)CH=CH₂ , 3-methyl-1,4-pentadiene, abbreviated structural formula

skeletal formula, no E/Z or R/S isomers possible.

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) : 2 (1+1) : 1 : 3 (for equivalent protons of the principal chemical shifts)

Four NMR peaks despite symmetry of this molecule.

 

(21) 2-methylpenta-2,3-diene, CH₃CH=C=C(CH₃)₂ , 2-methyl-2,3-pentadiene, abbreviated structural formula

skeletal formula, no E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

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

 

(22) 2,3-dimethylbuta-1,3-diene, H₂C=C(CH₃)C(CH₃)=CH₂ , 2,3-dimethyl-1,3-butadiene, abbreviated structural formula

skeletal formula, no E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2+2) : 6 (3+3) = 2 : 3 (for equivalent protons of the principal chemical shifts), reduced number of NMR peaks due to symmetry of molecule.

 

(23-61) Cycloalkenes - aliphatic compounds with a C=C double bond in a ring (alicyclic)

(23) cyclohexene, , skeletal formula, no E/Z or R/S isomers possible.

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

¹H NMR ratio of peaks: 4 (2+2) : 4 (2+2) : 2 (1+1) (for equivalent protons of the principal chemical shifts), reduced number of NMR peaks due to symmetry of molecule.

 

(24) 1-methylcyclopentene, , 1-methylcyclopent-1-ene, skeletal formula,

No E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 2 : 3 (clockwise for equivalent protons of the principal chemical shifts)

 

(25) 3-methylcyclopentene, , 3-methylcyclopent-1-ene, skeletal formula

NOT 2-methylcyclopentene, because the carbon atoms of the C=C are preferentially numbered 1,2.

No E/Z isomers, but R/S isomers based on the right-hand carbon atom of the pentangle, C3, which is chiral.

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 1 : 3 : 1 (clockwise for equivalent protons of the principal chemical shifts)

 

(26) 4-methylcyclopentene, , 4-methylcyclopent-1-ene, skeletal formula

No E/Z or R/S isomers possible.

NOT 3-methylcyclopropene, because the carbon atoms of the C=C are preferentially numbered 1,2.

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+1) : 4 (2+2) : 1 : 3 (for equivalent protons of the principal chemical shifts)

 

(27) 1-ethylcyclobutene, , 1-ethylcyclobut-1-ene, 1-ethyl-1-cyclbuttene,

The skeletal formula and there are no E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 2 : 1 : 2 : 3 (clockwise for equivalent protons of the principal chemical shifts)

 

(28) 3-ethylcyclobutene, , 3-ethylcyclobut-1-ene, skeletal formula

No E/Z isomers, but R/S isomers based on the bottom left carbon atom of the □, C3 is chiral.

NOT 2-ethylcyclopropene because the C=C carbon atoms are preferentially numbered 1 and 2.

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

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

 

(29) 1,2-dimethycyclobutene, , 1,2-dimethylcyclobut-1-ene, skeletal formula.

No E/Z or R/S isomerism possible.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2+2) : 6 (3+3) (for equivalent protons of the principal chemical shifts), reduced number of NMR peaks due to symmetry.

 

(30a) 1,3-dimethylcyclobutene, , 1,3-dimethylcyclobut-1-ene, skeletal formula.

R/S isomerism possible based on the top left carbon atom of the □, C3, which is chiral.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 1 : 3 : 1 : 3 (for equivalent protons of the principal chemical shifts)

 

(30b) 2,3-dimethylcyclobutene , , 2,3-dimethylcyclobut-1-ene

Also named as 1,4-dimethylcyclobutene or 1,4-dimethylcyclobut-1-ene

R/S isomerism possible based on the bottom left carbon atom of the □, C3, which is chiral.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(31) 3,3-dimethylcyclobutene, , 3,3-dimethylcyclobut-1-ene, skeletal formula

No E/Z or R/S isomerism possible.

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

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

 

(32) 3,4-dimethylcyclobutene, , 3,4-dimethylcyclobut-1-ene, skeletal formula

E/Z (cis/trans) isomerism possible based on the two ring methyl groups, but the left C atoms of the ring are both chiral so is R/S isomerism is possible?

Overlap of types of stereoisomerism (university level analysis)

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

(Z)-3,4-dimethylcyclbutene (cis isomer), , a = a = CH₃

(E)-3,4-dimethylcyclbutene (trans isomer) , , a = a = CH₃

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

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

 

(33) 1-propylcyclopropene, , 1-propylcycloprop-1-ene, skeletal formula

No E/Z or R/S isomerism possible.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(34) 3-propylcyclopropene, , 3-propylcycloprop-1-ene, skeletal formula

NOT 2-propylcyclopropene because the C=C carbon atoms are preferentially numbered 1 and 2.

No E/Z or R/S isomerism possible.

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) : 1 : 2 : 2 : 3 (for equivalent protons of the principal chemical shifts)

 

(35) 1-(1-methylethyl)cyclopropene ?, , skeletal formula

No E/Z or R/S isomerism possible.

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

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

 

(36) 3-(1-methylethyl)cyclopropene ?, , skeletal formula

No E/Z or R/S isomerism possible.

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+1) : 1 : 1 : 6 (3+3) (for equivalent protons)

 

(37) 1-ethyl-2-methylcyclopropene, , 1-ethyl-2-methylcycloprop-1-ene, skeletal formula

No E/Z (?) or R/S isomerism possible.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 2 : 3 (for equivalent protons of the principal chemical shifts)

 

(38) 1-ethyl-3-methylcyclopropene, , 1-ethyl-3-methylcycloprop-1-ene, skeletal formula

NOT 1-ethyl-2-methylcyclopropene because the C=C carbon atoms are preferentially numbered 1 and 2.

R/S isomerism possible, based on top carbon atom of the ∆, which is chiral.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(39) 3-ethyl-1-methylcyclopropene, , 3-ethyl-1-methylcycloprop-1-ene, skeletal formula

R/S isomerism possible, based on top carbon atom of the ∆, which is chiral.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(40) 3-ethyl-3-methylcyclopropene, , 3-ethyl-3-methylcycloprop-1-ene, skeletal formula

NOT 2-ethyl-2-methylcyclopropene because the C=C carbon atoms are preferentially numbered 1 and 2.

No E/Z or R/S isomers possible of this cycloalkene.

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

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

 

(41) 1,2,3-ttrimethylcyclopropene, , 1,2,3-trimethycycloprop-1-ene, skeletal formula

No E/Z or R/S isomers possible.

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 : 3 (for equivalent protons)

 

(42) 1,3,3-trimethylcyclopropene, , 1,3,3-trimethylcycloprop-1-ene, skeletal formula

NOT 1,2,2-trimethylcyclopropene because the C=C carbon atoms are preferentially numbered 1 and 2.

No E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

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

 

(43) bicyclo[2.2.0]hexane, , skeletal formula

E/Z or R/S isomers possible due to symmetry?

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 2 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 8 (4x2) : 2 (1+1) = 4 : 1 (for equivalent protons)

Note that this isn't it's real shape!, it is 'crumpled' so that all the C-C-C, C-C-H and H-C-H bond angles are ~109^o.

 

(44) bicyclo[3.1.0]hexane, , skeletal formula

No E/Z isomers possible?, but R/S isomers?

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

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

 

(45) 2,4-dimethylbicyclo[1.1.0]butane, , skeletal formula

No E/Z or R/S isomers possible.

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

¹H NMR ratio of peaks: 6 (3+3) : 2 (1+1) : 2 (1+1)  (for equivalent protons of the principal chemical shifts), reduced NMR peaks due to symmetry of molecule.

 

(46) methylidenecyclopentene, , skeletal formula

No E/Z or R/S isomers possible.

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) : 4 (2+2) : 2 (for equivalent protons of the principal chemical shifts)

 

(47) ethylidenecyclobutane, , skeletal formula

No E/Z or R/S isomers possible.

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

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

 

(48) ethenylcyclobutane, , skeletal formula, cyclobutylethene ?

No E/Z or R/S isomers possible.

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

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

 

(49) 1-methyl-2-methylenecyclobutane, , skeletal formula

R/S isomers possible based on the top left carbon atom, which is chiral.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(50) 1-methyl-3-methylenecyclobutane, , skeletal formula

No E/Z or R/S isomers possible.

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 : 4 (2+2) : 2 (for equivalent protons)

 

(51) name ?, , skeletal formula

No E/Z or R/S isomers possible.

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

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

 

(52) 1-cyclopropylpropene, , skeletal formula

Other names: 1-cyclopropylprop-1-ene, 1-cyclopropyl-1-propene, (E)-1-cyclopropylpropene, (Z)-1-cyclopropylpropene, (E)-1-cyclopropylprop-1-ene, (E)-1-cyclopropyl-1-propene, (Z)-1-cyclopropylprop-1-ene, (Z)-1-cyclopropyl-1-propene

E/Z geometrical isomers possible based on the C=C bond.

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

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

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

 

(53) name ?, , skeletal formula

No E/Z or R/S isomers possible.

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

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

 

(54) 3-cyclopropylpropene, , skeletal formula.

3-cyclopropylprop-1-ene, 3-cyclopropyl-1-propene

No E/Z or R/S isomers possible.

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

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

 

(55) name ?, , skeletal formula

No E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2+2) : 6 (3+3) (for equivalent protons of the principal chemical shifts, reduced number due to high symmetry of molecule)

 

(56) 1-ethylidene-2-methylcyclopropane, , skeletal formula

(E)-1-ethylidene-2-methylcyclopropane, (Z)-1-ethylidene-2-methylcyclopropane

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

Both E/Z isomers based on the alkene bond and R/S stereoisomers based on the bottom right carbon atom of the ∆, which is chiral - complicated situation - university level.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(57) 1-ethenyl-1-methylcyclopropane, , skeletal formula

No E/Z or R/S isomers possible.

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

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

 

(58) 1-ethenyl-2-methylcyclopropane, , skeletal formula

E/Z (geometrical) isomers based on the two substituents in the cyclopropane ring and R/S stereoisomers based on the bottom right carbon atom of the ∆, which is chiral.

This is complicated stereoisomerism - university level analysis.

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

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

 

(59) 1-ethyl-2-methylenecyclopropane ?,  , skeletal formula

2-ethyl-1-methylenecyclopropane ?

R/S isomers based on the bottom right carbon atom of the ∆, which is chiral.

This is complicated stereoisomerism!

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

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

 

(60) 1,1-dimethyl-2-methylenecyclopropane ?, , skeletal formula

2,2-dimethyl-2-methylenecyclopropane ?

No E/Z or R/S isomers possible.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

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

 

(61) 1,2-dimethyl-3-methylenecyclopropane, , skeletal formula

Based on the two bottom carbon atoms of the ∆, both E/Z and R/S stereoisomerism possible, very complicated, university level.

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) : 2 (1+1) : 2 (for equivalent protons)

 

(62-?) I'm sure there are other isomers possible for C₆H₁₀, but I think I've illustrated enough examples?

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(3) EXTRA NOTES on the isomers of Molecular Formula: C₆H₁₀

• Degrees of unsaturation: 2

• This allows for:

  • Alkyne isomers (one triple bond)

  • Cycloalkene isomers (one ring + one double bond)

  • Diene isomers (two double bonds)

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Types of Isomerism in C₆H₁₀

Type of Isomerism	Description
Constitutional	Different connectivity: e.g. hex-1-yne versus 1,3-cyclohexadiene
Positional	Triple or double bond in different locations (e.g. hex-1-yne versus hex-2-yne)
Chain (skeletal)	Straight versus branched carbon skeletons (e.g. 3-methylpent-1-yne)
Geometric (E/Z)	For alkenes with two different groups on each C=C (e.g. hex-2-ene)
Ring versus acyclic	Cycloalkenes versus open-chain alkynes/dienes
Conformational	Chair/boat forms in cyclohexenes; rotamers in branched chains

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Representative Constitutional Isomers of C₆H₁₀

Alkyne Isomers

• Hex-1-yne

• Hex-2-yne

• 3-Methylpent-1-yne

• 3-Methylpent-2-yne

• 2-Methylpent-1-yne

Cycloalkene Isomers

• Cyclohexene

• Methylcyclopentene (1- or 2-substituted)

• 1,3-Cyclohexadiene

• 1,4-Cyclohexadiene

Diene Isomers

• Hexa-1,3-diene (conjugated)

• Hexa-1,4-diene (non-conjugated)

• 2-Methylpenta-1,3-diene

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Differences in Physical Properties of selected isomers of C₆H₁₀

Property	Alkyne Isomers	Cycloalkenes	Dienes
Boiling Point	Lower for terminal alkynes	Higher due to ring strain relief	Conjugated dienes slightly lower
Polarity	Terminal alkynes more polar	Cycloalkenes less polar overall	Conjugation affects dipole moment
Spectroscopy	C≡C stretch ~2100–2260 cm⁻¹	C=C stretch ~1640 cm⁻¹	IR shifts lower with conjugation

Good point about different infrared wavenumbers.

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Differences in Chemical Reactivity of selected isomers of C₆H₁₀

Reaction Type	Alkyne Isomers	Cycloalkenes	Dienes
Electrophilic Addition	Terminal alkynes undergo Markovnikov	Cyclohexene reacts like typical alkene	Conjugated dienes show 1,2 & 1,4 addition
Hydrogenation	Converts to alkene then alkane	Converts to cyclohexane	Conjugated dienes hydrogenate selectively
Diels–Alder	Not applicable	Rare unless conjugated	Conjugated dienes are reactive partners
Acidity	Terminal alkynes are weakly acidic	Not acidic	Dienes not acidic but reactive

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Uses and Applications of selected isomers of C₆H₁₀

• Alkynes: Precursors in organic synthesis (e.g. Sonogashira coupling), fuel additives, welding gases (ethyne).

• Cycloalkenes: Used in polymer synthesis, fragrance intermediates, and as models for ring strain.

• Dienes: Key monomers in synthetic rubber (e.g. 1,3-butadiene), Diels–Alder chemistry, and fine chemical synthesis.

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Student Misconceptions about  selected isomers of C₆H₁₀

• “Alkynes are just like alkenes” — No! Alkynes have linear geometry and different reactivity (e.g. acidity, triple bond additions).

• “Conjugated dienes react the same as isolated ones” — False. Conjugation stabilizes intermediates and changes regioselectivity.

• “Cyclohexene is aromatic” — Incorrect. It lacks full conjugation and planarity needed for aromaticity.

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Exam Revision Tips for questions involving selected isomers of C₆H₁₀

• Draw and name all major isomers: practice IUPAC naming and skeletal structures.

• Compare reactivity: use mechanisms to explain why conjugated dienes undergo 1,4-addition.

• Spectroscopy practice: identify IR stretches for C≡C and C=C; predict NMR shifts for vinylic and allylic protons.

• Mechanism mastery: show electrophilic addition to alkynes and dienes with regioselectivity.

• Use energy profiles: explain why conjugated systems are more stable and react differently.

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(4) Learning objectives - questions to be answered?

How do you work out the structure of the isomers of molecular formula C6H10?

How do you draw the structural formula and skeletal formula of the isomers of molecular formula C6H10?

How many aliphatic structural isomers are there of molecular formula C6H10?

How many aliphatic carbon chain isomers are there of molecular formula C6H10?

How many positional isomers are there of molecular formula C6H10?

How many E/Z (geometrical) isomers are there of molecular formula C6H10?

How many R/S (optical) isomers (enantiomers) of molecular formula C6H10?

Are there any aliphatic open chain alkene isomers of molecular formula C6H10?

Are there any diene isomers of molecular formula C6H10?

Are there any alkyne isomers of molecular formula C6H10?

Are there any alicyclic cycloalkane isomers of molecular formula C6H10?

Are there any alicyclic cycloalkene isomers of molecular formula C6H10?

Are there any functional group isomers with a molecular formula C6H10?

Are there any E/Z (geometrical) isomers with a molecular formula C6H10?

Are there any R/S (optical) isomers (enantiomers) with a molecular formula C6H10?

Does C6H10 have any stereoisomers?

This page will answer these questions for molecular formula C₆H₁₀

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(5) QUESTIONS Practise exam questions based on isomers of molecular formula C6H10 Jot down your responses and check out the answers  ANSWERS to the questions based on the isomers of C6H10 If you think there are any errors, please email me asap at chem55555@hotmail.com I don't mind if students/teachers do a selected printout of these questions and answers. Give the seven selected isomers of molecular formula C6H10 ... A B C D E F G Q1 Which isomer(s) of C6H10 will readily add a maximum of one bromine molecule per molecule? Q2 Which isomer(s) of C6H10 can exhibit E/Z (geometrical) isomerism? Q3 Which isomer(s) of C6H10 will not readily accept a bromine molecule in an addition reaction? Q4 Which isomer(s) of C6H10 can add two molecules of hydrogen in a hydrogenation reaction? Q5 Which isomer(s) of C6H10 can exhibit R/S (optical) isomerism? Q6 Which isomer(s) of C6H10 are alkynes? Q7 (a) Using abbreviated structural formula, write equations for B and D reacting with excess bromine (b) IUPAC name the products in each case, and, what if any, do the products exhibit any type of isomerism? If you think there are any errors, please email me asap at chem55555@hotmail.com

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Associated organic chemistry  links

INDEX of ALL revision notes on the chemistry ALKENES including reactions and polymers

For isomerism in organic chemistry, see also the notes

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(5) ANSWERS Practise exam questions based on isomers of molecular formula C6H10 If you think there are any errors, please email me asap at chem55555@hotmail.com I don't mind if students/teachers do a selected printout of these questions and answers. Give the seven selected isomers of molecular formula C6H10 ... A B C D E F G Q1 Which isomer(s) of C6H10 will readily add a maximum of one bromine molecule per molecule? ANSWERS A, C and E, each molecule has a single C=C bond, albeit in a cycloalkene ring. Q2 Which isomer(s) of C6H10 can exhibit E/Z (geometrical) isomerism? ANSWER only B (which is an E (trans) isomer, based on the C=C bond of atoms C3 and C4). Q3 Which isomer(s) of C6H10 will not readily accept a bromine molecule in an addition reaction? ANSWER G only, all the others have an unsaturated C=C or C≡C bond. Note that G isn't that shape, it is 'crumpled' so that all bond angles are ~109o. Q4 Which isomer(s) of C6H10 can add two molecules of hydrogen in a hydrogenation reaction? ANSWERS B, D and F, these molecules have two C=C bonds or a single C≡C bond. Q5 Which isomer(s) of C6H10 can exhibit R/S (optical) isomerism? ANSWERS A and C, both have an asymmetric carbon atom, C3 in both cases (C1 and C2 form the C=C bond). Q6 Which isomer(s) of C6H10 are alkynes? ANSWER only D has a C≡C triple bond. Q7 (a) Using abbreviated structural formula, write equations for B and D reacting with excess bromine With two C=C double bonds, they will add two bromine molecules. For isomer B: CH3CH2CH=CHCH=CH2  +  2Br2  ===>  CH3CH2CHBrCHBrCHCH2Br For isomer D: CH3CH2CH2CH2C≡CH  +  2Br2  ===>  CH3CH2CH2CH2CBr2CHBr2 (b) IUPAC name the products in each case, and, what if any, do the products exhibit any type of isomerism? Product from B is 1,2,3,4-tetrabromohexane, positional isomerism of the bromine atoms, chain isomerism, R/S ('optical') isomerism (C2, C3 and C4 are chiral). Note that the product cannot now exhibit E/Z (geometrical) isomerism. Product from D is 1,1,2,2-tetrabromohexane,  positional isomerism of the bromine atoms, chain isomerism. If you think there are any errors, please email me asap at chem55555@hotmail.com