Question

$\mu _{obs}= \boldsymbol{\Sigma} \mu _ix_i $
where $\mu_i $ is the dipole moment of stable conformer and $x_i $ is
the mole fraction of that conformer.
(a) Write stable conformer for $Z-CH_2-CH_2-Z \, in $
Newman's projection.
If $\mu _{solution}=1.0 \, D $ and mole fraction of anti form = 0.82,
find $\mu _{gauche} $
(b) Write most stable meso conformer of $(CHDY)_2. $ If
(i) $Y=CH_3 $ about $C_2-C_3 $ rotation and
(ii) Y=OH about $C_1-C_2 $ rotation.

Answer 1

Mole fraction of anti form = 0.82
Mole fraction of gauche form = 0.18
$ \mu _{obs}=1 D $
$\Rightarrow 1=\mu _{anti} \times 0.82+ \mu _{gauche} \times 0.18 $
$\because \mu _{anti}=0 $
$\Rightarrow 1=\mu _{gauche} \times 0.18 $
$\Rightarrow \mu _{gauche} = \frac {1}{0.18}=5.55 \, D $
Structure (ii) is more stable than its anti conformer because of
intramolecular H-bonding.