-3
$\begingroup$

why 2,2-dimethylpropane is not called isopentane? since 2-methylpropane is called isobutane

$\endgroup$
  • 1
    $\begingroup$ ... because it is not the only isomer of n-pentane. $\endgroup$ – Karl Apr 7 '18 at 10:12
  • 3
    $\begingroup$ It's called neopentane, typically 2-(mono)methylalkanes are called iso. $\endgroup$ – Mithoron Apr 7 '18 at 14:29
  • $\begingroup$ @Mithoron Yes; except the famous “isooctane” which is used for the determination of the octane rating of fuel. This isomer of octane is actually 2,2,4-trimethylpentane. $\endgroup$ – Loong Apr 7 '18 at 16:30
  • $\begingroup$ @Loong Indeed, calling in isoneo would be complicated ;D $\endgroup$ – Mithoron Apr 7 '18 at 18:44
3
$\begingroup$

In common nomenclature, the prefix 'iso-' is applied when the chain of carbons is continuous bar one methyl group. The example you provided, 2-methylpropane, is observed to be continuous with exception to one methyl group bound to the central carbon atom.

However, 2,2-dimethylpropane does not feature an analogous structure: because two methyl groups are bound to the central carbon, the same classification is inapplicable. In place, the molecule could be labelled as 'neopentane', in which the prefix specifies a continuous chain excepting two alkyl groups.

Isopentane

The above image is 2-methylbutane, or isopentane.

Neopentane

The above-shown image is 2,2-dimethylpropane, or neopentane

If you desire further information concerning the nomenclature, I would advise the following link, from which these images were extracted: http://www.chem.ucla.edu/~harding/IGOC/C/common_name.html

$\endgroup$
  • 2
    $\begingroup$ Which is "isohexane"? 2-methylpentane or 3-methylpentane? If I am not mistaken "iso-n-ane" is generally applied to 2-methyl-(n-1)-ane. $\endgroup$ – Oscar Lanzi Apr 7 '18 at 11:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.