How can I draw Sawhorse projections for the #C_2-C_3# bond of hexane?

1 Answer
Jan 23, 2015

You can find the general procedure for drawing sawhorse projections at this location.

The condensed structural formula of hexane is CH₃-CH₂CH₂-CH₂CH₂CH₃.

Its bond-line structure is

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Step 1. Convert the bond-line structure to a wedge-dash structure at C-2 and C-3.

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Step 2. Convert the wedge-dash structure to a sawhorse projection.

We must look at the molecule along the C2-C3 bond (from the lower left).

The three bonds nearest us form an inverted "Y".

We draw a sawhorse template with the C2-C3 bond going from lower left to upper right.

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Next we add the atoms.

The groups on C-2 are CH₃, H, and H.
The groups on C-3 are CH₃CH₂CH₂, H, and H.

On C-2, we put the bulky CH₃ group at the top of the inverted "Y",
On C-3, we put the bulky CH₃CH₂CH₂ group at the bottom of the "Y", with the H atoms on the other two bonds.

This staggered conformation puts the two bulky groups anti to each other and is the most stable form.

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To get the two gauche forms, hold the front carbon in in place and rotate the back carbon in 120° increments. You get an enantiomeric pair of rotational isomers:

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