Organic Chemistry Basics 1 Question 39
45. $\mu_{\mathrm{obs}}=\Sigma \mu_{i} x_{i}$
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 $Z-\mathrm{CH}{2}-\mathrm{CH}{2}-\mathrm{Z}$ in Newman’s projection.
If $\mu_{\text {solution }}=1.0 \mathrm{D}$ and mole fraction of anti form $=0.82$, find $\mu_{\text {gauche }}$
(b) Write most stable meso conformer of $(\mathrm{CHDY})_{2}$. If
(i) $Y=\mathrm{CH}{3}$ about $\mathrm{C}{2}-\mathrm{C}_{3}$ rotation and
(ii) $Y=\mathrm{OH}$ about $\mathrm{C}{1}-\mathrm{C}{2}$ rotation.
$(2005,6 M)$
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Solution:
- (a)
anti
gauche
Mole fraction of anti form $=0.82$
Mole fraction of gauche form $=0.18$
$$ \begin{array}{rlrl} & \mu_{\mathrm{obs}} & =1 \mathrm{D} \ \Rightarrow & 1 & =\mu_{\text {anti }} \times 0.82+\mu_{\text {gauche }} \times 0.18 \ \because & & \mu_{\text {anti }} & =0 \Rightarrow 1=\mu_{\text {gauche }} \times 0.18 \ \Rightarrow & & \mu_{\text {gauche }}=\frac{1}{0.18}=5.55 \mathrm{D} \end{array} $$
(b)
(i)
(ii) Structure (ii) is more stable than its anti conformer because of intramolecular H-bonding.
