Naming Alkanes with Alkyl Groups

Chemistry Level 1

Name the alkane above.

3-ethyl-2-methylpentane 2-methylpentane 2-methylhexane 2-methyl-3-ethyl-pentane

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Nicole Ling by Nicole Ling , 24, Malaysia

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3 solutions

Raj Magesh
Apr 23, 2014

Four simple things to do:

  1. Identify the longest carbon chain: here, it is 5 atoms long; hence, the backbone is pentane .
  2. Identify any alkyl substituents: here, there is one ethyl group and one methyl group.
  3. Use the first-point-of-difference rule: here, numbering should start from the right, making it 3-ethyl and 2-methyl and NOT 3-ethyl and 4-methyl.
  4. Finally, alphabetize: e thyl comes before m ethyl, making the final answer 3-ethyl-2-methylpentane
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Is it necessary to alphabetize?

Rashi Kumar - 7 years, 1 month ago

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Yeah, otherwise we end up with two possible names for the compound, something we always try to avoid.

Raj Magesh - 7 years, 1 month ago

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Thanks Raj, I wasn't knowing this.

Rashi Kumar - 7 years, 1 month ago

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@Rashi Kumar – No prob =)

Raj Magesh - 7 years, 1 month ago

But remember: The prefixes of some functional groups, such as iso , will not be included in the alphabetize step.

For example, i sopropyl will come before m ethyl. But the prefix iso will not be included in this step, so m ethyl will come before i sopropyl

Dang Anh Tu - 7 years ago
Sagnik Ghosh
May 18, 2014

1)Identify the longest carbon chain: here, it is 5 atoms long; hence, the backbone is pentane. 2)Identify any alkyl substituents: here, there is one ethyl group and one methyl group. 3)Numbering should start from the right, making it 3-ethyl and 2-methyl and NOT 3-ethyl and 4-methyl as least possible no. should be assigned. Finally, alphabetize: ethyl comes before methyl, making the final answer 3-ethyl-2-methylpentane

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Here the given structure of the hydrocarbon is a five carbon chain structure hence it is pentane.

It is bonded to two alcoholic ethyl and methyl groups CH3-CH2 and CH3 respectively.

By numbering from the right, we can find the position of these alcoholic groups as 3-ethyl and 2-methyl groups respectively.

Hence the name of this alkane is 3-ethyl-2-methylpentane

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sir if we have a compound containing 3 carboxylic acid.2 are on terminals and other on the chain from where the numbering will start

sudheendra nadagoud - 7 years, 1 month ago

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