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.
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.
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
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