In the fully eclipsed conformation of butane (viewed along the C2-C3 bond) the dihedral angle between the two $CH X_{3}$ groups is

A $0^{\circ}$
B $6 0^{\circ}$
C $12 0^{\circ}$
D $18 0^{\circ}$

Answer: A

In the fully eclipsed (syn-periplanar) conformation the two methyl groups lie directly behind one another in the Newman projection, so the dihedral angle is

0^{\circ}

6 0^{\circ}

is gauche and

18 0^{\circ}

is anti.

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In the fully eclipsed conformation of butane (viewed along the C2-C3 bond) the dihedral angle between the two CHX3​ groups is

Answer: A

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In the fully eclipsed conformation of butane (viewed along the C2-C3 bond) the dihedral angle between the two $CH X_{3}$ groups is