Common Branched Alkyl Groups

Common Branched Alkyl Group

A branched alkyl substituent having a widely used retained common name.

Isopropyl

A three-carbon alkyl group with structure (CH₃)₂CH–; its systematic substituent name is 1-methylethyl.

Isopropyl Abbreviation

i-Pr

sec-Butyl

A four-carbon alkyl group attached through a secondary carbon; its systematic substituent name is 1-methylpropyl.

sec-Butyl Abbreviation

sec-Bu

Isobutyl

A four-carbon branched alkyl group with structure (CH₃)₂CHCH₂–; its systematic substituent name is 2-methylpropyl.

tert-Butyl

A four-carbon branched alkyl group with structure (CH₃)₃C–; its systematic substituent name is 1,1-dimethylethyl.

tert-Butyl Abbreviation

t-Bu

Isopentyl (Isoamyl)

A five-carbon branched alkyl group with structure (CH₃)₂CHCH₂CH₂–; also called isoamyl and systematically named 3-methylbutyl.

Isopentyl (Isoamyl) Abbreviation

i-amyl

Neopentyl

A five-carbon branched alkyl group with structure (CH₃)₃CCH₂–; its systematic substituent name is 2,2-dimethylpropyl.

tert-Pentyl (tert-Amyl)

A five-carbon branched alkyl group with structure (CH₃)₂C(CH₂CH₃)–; also called tert-amyl and systematically named 1,1-dimethylpropyl.

tert-Pentyl (tert-Amyl) Abbreviation

t-amyl

Meaning of sec- in an Alkyl Name

Indicates that the alkyl group is attached through a secondary carbon.

Meaning of tert- in an Alkyl Name

Indicates that the alkyl group is attached through a tertiary carbon.

Meaning of iso- in a Common Alkyl Name

A retained prefix describing a characteristic branched carbon skeleton; it does not by itself specify the degree of the attachment carbon.

Alphabetization of iso-

The prefix iso- is included when alphabetizing a substituent name.

Alphabetization of sec-

The prefix sec- is ignored when alphabetizing a substituent name.

Alphabetization of tert-

The prefix tert- is ignored when alphabetizing a substituent name.

Alphabetization Rule for iso-, sec-, and tert-

Count iso- when alphabetizing; ignore sec- and tert-.

4-Isopropylheptane

A heptane parent chain with an isopropyl substituent at carbon 4.

4-(1-Methylethyl)heptane

The systematic-name form corresponding to 4-isopropylheptane.

Common Name vs. Systematic Name of a Branched Substituent

A branched substituent may have both a retained common name, such as isopropyl, and a systematic name, such as 1-methylethyl.

Recognizing Isopropyl

Look for a point-of-attachment carbon bonded to two CH₃ groups: (CH₃)₂CH–.

Recognizing sec-Butyl

Look for a four-carbon unbranched skeleton attached through an internal secondary carbon: CH₃CH(–)CH₂CH₃.

Recognizing Isobutyl

Look for the pattern (CH₃)₂CHCH₂–, with attachment through CH₂.

Recognizing tert-Butyl

Look for a point-of-attachment carbon bonded to three CH₃ groups: (CH₃)₃C–.

Recognizing Neopentyl

Look for attachment through CH₂ directly bonded to a carbon bearing three CH₃ groups: (CH₃)₃CCH₂–.

3-Isopropyl-2-methylhexane

A hexane parent chain containing a methyl substituent at carbon 2 and an isopropyl substituent at carbon 3.

Drawing 3-Isopropyl-2-methylhexane

Start with a six-carbon hexane chain, place methyl at C2, and place isopropyl at C3.