The 75 alkane carbon chain constitutional-structural isomers of molecular formula C₁₀H₂₂ (M_r = 142)

Introduction to 75 constituent isomers of C₁₀H₂₂

Percent composition based on atomic masses C= 12.01  H = 1.01  and  M_r(C₁₀H₂₂) = 142.32

Element composition (to two dp): carbon = 84.39%     hydrogen = 15.61%

Empirical formula = C₅H₁₁ and molecular formula = C₁₀H₂₂

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

Only carbon chain structural isomerism applies to the isomers of C₁₀H₂₂.

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

E/Z stereoisomerism was called 'geometrical isomerism' e.g. cis and trans isomers of alkenes or disubstituted cyclic alkanes where there are 3D spatial variations due to restricted bond rotation that are not mirror images and not super imposable.

Does NOT apply to the isomers of C₁₀H₂₂.

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. 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 many examples of R/S 'optical' isomerism in the isomers of C₁₀H₂₂.

AND, some have two chiral centres, giving a possible permutation of 4 stereoisomers for the same molecule (RR', RS', SR' and SS), or just 3 if the molecule is symmetrical with respect to the two chiral centres (R, S and optically inactive meso stereoisomers).

NOTE

These are all examples of carbon chain isomerism, but a number of them, theoretically, will exhibit R/S isomerism (mirror image optical isomers known as enantiomers).

For benzene ring isomers of C₁₀H₂₂ the side chains are methyl, ethyl or propyl groups.

Many of these structural isomers also exhibit R/S (optical isomerism) with pairs of enantiomers.

I have identified 75 constitutional isomers, are there others I haven't spotted?

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Details of the constitutional isomers of C₁₀H₂₂ (and the accompanying R/S 'optical' isomers)

(1) decane, CH₃CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₃  or  CH₃(CH₂)₈CH₃  for brevity!

skeletal formula

A linear alkane hydrocarbon molecule, only one possible from a given alkane molecular formula.

 

Details of isomers based on a carbon chain of nine (substituted nonanes)

(2) 2-methylnonane, CH₃CH₂CH₂CH₂CH₂CH₂CH₂CH(CH₃)₂

skeletal formula

(3) 3-methylnonane, CH₃CH₂CH₂CH₂CH₂CH₂CH(CH₃)CH₂CH₃  (R/S optical isomers, 3rd C is chiral)

skeletal formula

(4) 4-methylnonane, CH₃CH₂CH₂CH₂CH₂CH(CH₃)CH₂CH₂CH₃  (R/S optical isomers, 4th C is chiral)

skeletal formula

(5) 5-methylnonane, CH₃CH₂CH₂CH₂CH(CH₃)CH₂CH₂CH₂CH_{3 (symmetrical molecule)}

skeletal formula

 

Details of isomers based on a carbon chain of eight (substituted octanes)

(6) 3-ethyloctane, skeletal formula,  

(7) 4-ethyloctane, skeletal formula, (R/S optical isomers, 4th C is chiral)

(8) 2,2-dimethyloctane, skeletal formula,  

(9) 2,3-dimethyloctane, skeletal formula,   (R/S optical isomers, 3rd C is chiral)

(10) 2,4-dimethyloctane, skeletal formula, (R/S optical isomers, 4th C is chiral)

(11) 2,5-dimethyloctane, skeletal formula, (R/S optical isomers, 5th C is chiral)

(12) 2,6-dimethyloctane, skeletal formula, (R/S optical isomers, 6th C is chiral)

(13) 2,7-dimethyloctane, skeletal formula,  

(14) 3,3-dimethyloctane, skeletal formula,

(15) 3,4-dimethyloctane, skeletal formula,

R/S optical isomers, 3rd and 4th C atoms are chiral - complicated, university level analysis - no plane of symmetry in the molecule, so four permutations of stereoisomers possible: RR', RS', SR' and SS'

(16) 3,5-dimethyloctane, skeletal formula,

R/S optical isomers, 3rd and 5th C atoms are chiral - complicated, university level analysis - no plane of symmetry in the molecule, so four permutations of stereoisomers possible: RR', RS', SR' and SS'

(17) 3,6-dimethyloctane, skeletal formula,

R/S optical isomers, 3rd and 6th C atoms are chiral, symmetrical molecule - plane of symmetry, so there are a pair of R/S optical isomers (enantiomer) and a 3rd meso form stereoisomer.

(18) 4,4-dimethyloctane, skeletal formula,

(19) 4,5-dimethyloctane, skeletal formula,

R/S optical isomers, 4th and 5th C atoms are chiral, symmetrical molecule - plane of symmetry, so there are a pair of R/S optical isomers (enantiomer) and a 3rd meso form stereoisomer.

 

Details of isomers based on a carbon chain of seven (substituted heptanes)

(20) 4-propylheptane, skeletal formula

(21) 4-(1-methylethyl)heptane or 4-isopropylheptane,

(22) 3-ethyl-2-methylheptane, skeletal formula,

R/S optical isomers, 3rd C atom chiral

(23) 3-ethyl-3-methylheptane, skeletal formula,

(24) 3-ethyl-4-methylheptane, skeletal formula,

R/S optical isomers, 4th C atom chiral

(25) 3-ethyl-5-methylheptane, skeletal formula,

R/S optical isomers, 5th C atom chiral

(26) 4-ethyl-2-methylheptane, skeletal formula,

R/S optical isomers, 4th C atom chiral

(27) 4-ethyl-3-methylheptane, skeletal formula,   

R/S optical isomers, 3rd and 4th C atoms are chiral, no plane of symmetry - complicated, university level analysis - no plane of symmetry in the molecule, so four permutations of stereoisomers possible: RR', RS', SR' and SS'

(28) 4-ethyl-4-methylheptane, skeletal formula,

(29) 5-ethyl-2-methylheptane, skeletal formula,

R/S optical isomers, 5th C atom chiral

(30) 2,2,3-trimethylheptane, skeletal formula,  

R/S optical isomers, 3rd C atom chiral

(31) 2,2,4-trimethylheptane, skeletal formula,  

R/S optical isomers, 4th C atom chiral

(32) 2,2,5-trimethylheptane, skeletal formula,  

R/S optical isomers, 5th C atom chiral

(33) 2,2,6-trimethylheptane, skeletal formula,  

(34) 2,3,3-trimethylheptane, skeletal formula,

(35) 2,3,4-trimethylheptane, skeletal formula,  

R/S optical isomers, 3rd and 4th C atoms are chiral, no plane of symmetry - complicated, university level analysis - no plane of symmetry in the molecule, so four permutations of stereoisomers possible: RR', RS', SR' and SS'

(36) 2,3,5-trimethylheptane, skeletal formula,

R/S optical isomers, 3rd and 5th C atoms are chiral, no plane of symmetry - complicated, university level analysis - no plane of symmetry in the molecule, so four permutations of stereoisomers possible: RR', RS', SR' and SS'

(37) 2,3,6-trimethylheptane, skeletal formula,  

R/S optical isomers, 3rd C atoms is chiral

(38) 2,4,4-trimethylheptane, skeletal formula,

(39) 2,4,5-trimethylheptane, skeletal formula,

R/S optical isomers, 4th and 5th C atoms are chiral, no plane of symmetry - complicated, university level analysis - no plane of symmetry in the molecule, so four permutations of stereoisomers possible: RR', RS', SR' and SS'

(40) 2,4,6-trimethylheptane, skeletal formula,

(41) 2,5,5-trimethylheptane, skeletal formula,  

(42) 3,3,4-trimethylheptane, skeletal formula,  

R/S optical isomers, 4th C atoms is chiral

(43) 3,3,5-trimethylheptane, skeletal formula,  

R/S optical isomers, 5th C atoms is chiral

(44) 3,4,4-trimethylheptane, skeletal formula,  

R/S optical isomers, 3rd C atoms is chiral

(45) 3,4,5-trimethylheptane, skeletal formula,

 

Details of isomers based on a carbon chain of six (substituted hexanes)

(46) 2-methyl-3-(1-methylethyl)hexane or 3-isopropyl-2-methylhexane,

(47) 3,3-diethylhexane, skeletal formula,

(48) 3,4-diethylhexane, skeletal formula,

Some images included for isomers (49) to (57) were originally done for my alkanes nomenclature page, but the skeletal formula have been also in my new isomer image database. However, they are handy to show examples of how to write the abbreviated-condensed formula.

(49) 3-ethyl-2,2-dimethylhexane , ,   

R/S optical isomers, 3rd C is chiral, skeletal formula

(50) 3-ethyl-2,3-dimethylhexane , ,  

R/S optical isomers, 3rd C is chiral, skeletal formula

(51) 3-ethyl-2,4-dimethylhexane , ,  

R/S optical isomers, 3rd and 4th C are chiral, skeletal formula, skeletal formula

(52) 3-ethyl-2,5-dimethylhexane , ,  

R/S optical isomers, 3rd C is chiral, skeletal formula

(60) 2,2,3,5-tetramethylhexane, skeletal formula,

R/S optical isomers, carbon atom 3 is chiral

(61) 2,2,4,4-tetramethylhexane, skeletal formula,

(62) 2,2,4,5-tetramethylhexane, skeletal formula,

R/S optical isomers, carbon atom 4 is chiral

(63) 2,2,5,5-tetramethylhexane, skeletal formula,

(64) 2,3,3,4-tetramethylhexane, skeletal formula,

R/S optical isomers, carbon atom 4 is chiral

(65) 2,3,3,5-tetramethylhexane, skeletal formula,

(66) 2,3,4,4-tetramethylhexane, skeletal formula,

R/S optical isomers, carbon atom 3 is chiral

(67) 2,3,4,5-tetramethylhexane, skeletal formula,

R/S optical isomers, carbon atoms 3 and 4 are chiral, symmetrical molecule - plane of symmetry, so there are a pair of R/S optical isomers (enantiomer) and a 3rd meso form stereoisomer.

(68) 3,3,4,4-tetramethylhexane, skeletal formula,

 

 

Details of isomers based on a carbon chain of five (substituted pentanes)

(69) 2,4-dimethyl-3-(1-methylethyl)pentane or 3-isopropyl-2,4-dimethylpentane

skeletal formula,

(70) 3,3-diethyl-2-methylpentane, skeletal formula,

(71) 3-ethyl-2,2,3-trimethylpentane, skeletal formula,

(72) 3-ethyl-2,2,4-trimethylpentane, skeletal formula,

R/S optical isomers, carbon atom 3 is chiral

(73) 3-ethyl-2,3,4-trimethylpentane, skeletal formula,

(74) 2,2,3,3,4-pentamethylpentane, skeletal formula,

(75) 2,2,3,4,4-pentamethylpentane, skeletal formula,

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EXTRA NOTES on isomers of C₁₀H₂₂

Alkane isomers of molecular formula C₁₀H₂₂ (decane) are primarily used as fuels, solvents, and chemical feedstocks, with their applications shaped by branching and boiling point differences.

Straight-chain decane is favoured for combustion, while branched isomers serve in specialized fuels and industrial formulations.

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Overview of C₁₀H₂₂ Isomers

C₁₀H₂₂ represents the molecular formula for decane, a saturated hydrocarbon with 75 known structural isomers. These include:

• n-Decane: Straight-chain structure

• Branched isomers: e.g., 2-methylnonane, 3-ethyl-2-methyloctane, etc. some of which exhibit R/S optical isomerism.

Each isomer shares the same molecular formula but differs in structure, affecting physical properties like boiling point, density, and combustion behavior.

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Physical and Chemical Properties Comparison for isomers of C₁₀H₂₂

Property	n-Decane (Straight-chain)	Branched Isomers
Boiling Point	~174 °C	Lower (due to branching)
Density	~0.73 g/mL	Slightly lower
Combustion Efficiency	High	Moderate to high
Volatility	Lower	Higher
Surface Area	Larger	Smaller

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Applications by Isomer Type for isomers of C₁₀H₂₂

1. n-Decane (Straight-chain)

• Jet fuel & diesel additive: High energy density and clean combustion make it suitable for aviation and transport fuels.

• Combustion research: Used as a model compound to study hydrocarbon combustion kinetics.

• Solvent: Effective in organic synthesis and industrial degreasing due to its non-polar nature.

2. Branched Isomers

• Gasoline blending: Branched isomers have higher octane ratings, reducing engine knocking.

• Specialty fuels: Used in racing fuels and high-performance engines.

• Chemical intermediates: Serve as precursors in the synthesis of surfactants, lubricants, and plasticizers.

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Comparative Insights for isomers of C₁₀H₂₂

• Boiling Point & Volatility: Branched isomers boil at lower temperatures, making them more volatile and suitable for gasoline applications.

• Octane Rating: Branching increases octane number, enhancing anti-knock properties in internal combustion engines.

• Combustion Profile: n-Decane burns more uniformly, ideal for controlled combustion studies and diesel fuels.

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Industrial and Environmental Considerations for isomers of C₁₀H₂₂

• Fractional Distillation: C₁₀H₂₂ isomers are separated from crude oil via fractional distillation, with applications determined by boiling point and volatility.

• Environmental Impact: Combustion releases CO₂; thus, branched isomers with cleaner burn profiles are preferred in regulated fuel blends.

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Learning objectives - questions to be answered?

How many isomers are there of molecular formula C10H22?

How do you work out the structure of the isomers of molecular formula C10H22?

How do you draw the constitutional-structural formula of the isomers of molecular formula C10H22?

How do you draw the skeletal formula of the isomers of molecular formula C10H22?

How do you name the isomers of molecular formula C10H22?

How many aliphatic structural isomers are there of molecular formula C10H22?

How many aliphatic carbon chain isomers are there of molecular formula C10H22?

How many positional isomers are there of molecular formula C10H22?

Does C10H22 have any stereoisomers?

Are there any E/Z (geometrical) or RS (optical) stereoisomers (enantiomers) of C10H22?

Are there any aliphatic open chain alkene isomers of molecular formula C10H22?

Are there any alkane/cycloalkane isomers of molecular formula C10H22?

Are there any alkene/cycloalkene/diene/alkyne isomers of molecular formula C10H22?

Are there any alicyclic cycloalkane isomers of molecular formula C10H22?

Are there any functional group isomers with a molecular formula C10H22?

This page will answer these questions for molecular formula C₁₀H₂₂

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Associated organic chemistry  links

 Advanced Level pre-university organic chemistry notes

 IR, mass and H-1 & C-13 NMR spectra of organic compounds

Examples of effects of isomerism: The similarity or difference in the physical & chemical properties of structural isomers

Index of sets of isomers for a given molecular formula

The molecular structure and naming of ALKANES

Index of revision notes on the chemistry of ALKANES and the petrochemical industry

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

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

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 C10H22, Edexcel advanced level chemistry constitutional isomers of C10H22, OCR advanced level chemistry constitutional isomers of C10H22, IB advanced level chemistry constitutional isomers of C10H22, WJEC (Eduqas) advanced level chemistry constitutional isomers of C10H22, CIE Cambridge advanced level chemistry constitutional isomers of C10H22, US grade 11-12 AP honors chemistry courses  constitutional isomers of C10H22 and they will also prove useful to 1st year undergraduate students of chemistry including  constitutional isomers of C10H22.

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