The two alkane carbon chain structural isomers of molecular formula C₄H₁₀ (M_r = 58)

details below

Introduction to isomerism for molecular formula C₄H₁₀  (see also summary diagram)

Percent composition of C₄H₁₀ based on atomic masses C= 12.01  H = 1.01  and  M_r(C₄H₁₀) = 58.14

Element composition (to two dp): carbon = 82.63%     hydrogen = 17.37%

Empirical formula = C₂H₅ and molecular formula = C₄H₁₀

Structural isomerism  - isomers based on different connectivity's of the constituent atoms, so cannot be spatially identical (but 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.

Only (a) chain branching is applicable here.

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)

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 that are not mirror images and not super imposable.

Not applicable here.

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.

Not applicable here.

Note

These are open chain saturated aliphatic compounds called alkanes.

In terms of the carbon chain, butane would be described as 'linear' and methylpropane as 'branched'.

This is the first instant of the existence of structural isomers, (carbon chain isomers), for an alkane molecular formula with different carbon chain arrangements (chain isomerism), this is NOT possible with methane, ethane or propane.

No E/Z or R/S isomers possible, no stereoisomerism.

Molecular formula C₄H₁₀ is the first in the homologous alkane series C_nH_2n+2 to exhibit isomerism in any form.

Note that methane CH₄, ethane C₂H₆ and propane C₃H₈ cannot display any types of isomerism.

There are no E/Z or R/S stereoisomers and no functional group isomerism possible either.

There are 2 constitutional structural isomers of molecular formula C₄H₁₀, with no E/Z and R/S isomers, because there are just two possible carbon chain isomers for this aliphatic open chain alkane formula

(1)  or are abbreviated structural formulae for butane

 The skeletal formula is ,

the full displayed formula (ignoring bond angles!) is 

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

¹H NMR ratio of peaks: 6 (3+3) : 4 (2+2) = 3 : 2 (for equivalent protons)

See also spectra that can distinguish one C₄H₁₀ isomer from another

The infrared spectrum of butane

The infrared spectrum of 2-methylpropane

The mass spectrum of butane

The mass spectrum of 2-methylpropane

The H-1 NMR spectrum of butane

The H-1 NMR spectrum of 2-methylpropane

The C-13 NMR spectrum of butane

The C-13 NMR spectrum of 2-methylpropane

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

 

(2)  or are the abbreviated structural formula for 2-methylpropane

and the skeletal formula is

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

¹H NMR ratio of peaks: 9 (3x3) : 1 (for equivalent protons)

See also spectra links above.

Index of sets of isomers for a given molecular formula