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Leland Shenfield

Number of gauche interactions in an alkane

Benjamin Tsavkegh  Follow

When we sight down a carbon-carbon single bond and draw a Newman projection of a particular conformation, any two groups on the adjacent (vicinal) carbons that have a dihedral angle of 60° between them are said to have a gauche relationship.

In the following figure, the $\ce{X}$ and $\ce{Y}$ have a gauche relationship.

enter image description here

$\ce{X}$ and $\ce{Y}$ can be the same (they can both be methyl groups, other alkyl groups, other atoms such as halogen, etc.) or they can be different from each other. In most organic classes, the gauche interaction between methyl groups or alkyl groups is frequently discussed.

The answers you included (2,3,3) are correct. Looking at the middle molecule (b) in your figure, there are 3 gauche interactions. They are between

  • the front methyl and the back ethyl
  • the same front methyl and the back methyl
  • the other front methyl and the back methyl

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Douglas Scott  Follow
Youre welcome, glad to help out!More
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