The key difference between isobutyl and sec-butyl is that isobutyl group shows its branched structure at the second carbon atom of the carbon chain, whereas sec-butyl group shows its branched structure at the first carbon atom of the carbon chain.
The term butyl group refers to a four-carbon alkyl radical or substituent group having the chemical formula -C4H9. This functional group usually forms from one of butane’s two common isomers: n-butane or isobutane. The functional group that derives from n-butane is the n-butyl group which has a simple aliphatic carbon chain of four carbon atoms. However, if there is a carbon chain of three carbon atoms and a branch of the methyl group (a methyl substituent) that occurs at the first carbon atom (the carbon atom that is nearest to the R group or the vacant site of the functional group), then this functional group is named as sec-butyl group or secondary butyl group. The chemical formula for this type of butyl group is CH3-CH2CH(CH3)-.
CONTENTS
1. Overview and Key Difference
2. What is Isobutyl
3. What is Sec-butyl
4. Isobutyl vs Sec-butyl in Tabular Form
5. Summary – Isobutyl vs Sec-butyl
What is Isobutyl?
Isobutyl functional group is a four-carbon alkyl radical or functional group in which a three-membered carbon chain is attached to one methyl group at its second carbon atom. Therefore, this functional group contains a single methyl branch. The three-membered carbon chain contains a methyl group at the second carbon atom, while the third carbon atom has a vacant point to which a separate moiety of a molecule may attach with.
Figure 01: The Chemical Structure of Isobutyl Functional Group
The chemical formula for this group is CH3-CH(CH3)−CH2−, and the systematic name is “2-methyl propyl”. Ex: isobutyl acetate contains an isobutyl functional group attached to an acetate group. Moreover, isobutyl is a type of sec-butyl functional group.
What is Sec-butyl?
Sec-butyl group is a derivative of butyl functional group where there is a branched structure. Usually, a sec-butyl group consists of a three-carbon atom chain with a methyl substituent at the first carbon atom or the adjacent carbon atom to the vacant point of the functional group.
Figure 02: Sec-butyl Functional Group Chemical Structure
In addition, when the substituent is at first carbon atom, then it has the chemical formula CH3-CH2CH(CH3)- and the chemical name of the group is 1-methyl propyl.
What is the Difference Between Isobutyl and Sec-butyl?
Butyl functional group is a four-membered chain structure. There are different forms of butyl functional groups depending on the chemical structure. Isobutyl and sec-butyl are two such forms. The key difference between isobutyl and sec-butyl is that isobutyl group shows its branched structure at the second carbon atom of the carbon chain, whereas sec-butyl group shows its branched structure at the first carbon atom of the carbon chain. Isobutyl forms isobutyl compounds such as isobutyl alcohol while sec-butyl forms secondary-carbon compounds such as secondary alcohol. This is another difference between isobutyl and sec-butyl.
The following infographic presents the difference between isobutyl and sec-butyl in tabular form.
Summary – Isobutyl vs Sec-butyl
Butyl functional group is a four-membered chain structure. Isobutyl and sec-butyl are two forms of butyl functional groups. The key difference between isobutyl and sec-butyl is that isobutyl group shows its branched structure at the second carbon atom of the carbon chain, whereas sec-butyl group shows its branched structure at the first carbon atom of the carbon chain.
Reference:
1. “Butyl Group.” Wikipedia, Wikimedia Foundation.
2. Ashenhurst, James. “Don’t Be Futyl, Learn The Butyls.” Master Organic Chemistry, 22 Mar. 2021.
Image Courtesy:
1. “Isobutyl-Skeletal-SVG” By Darkness3560 – Own work (CC0) via Commons Wikimedia
2. “Sec-Butyl-Skeletal-SVG” By Darkness3560 – Own work (CC0) via Commons Wikimedia