Question

Which of the following molecule(s) is/are planar?

• A. $F_{2}C=C=C{F}_2$
• B. $F_{2}B-C\equiv C-B{F}_2$
• C. ${\left(Si{H}_3\right)}_{3}N$
• D. $N{H}_2-N{H}_2$

Answer 1

Answer: (B), (C)

The correct options are
B $F_{2}B-C\equiv C-B{F}_2$
C ${\left(Si{H}_3\right)}_{3}N$

(a) The given molecule is an allene with even number of $\pi$-bonds. So, the terminal $F$ atoms are in planes which are mutually perpendicular to each other.
(b) Terminal $-B{F}_2$ has $s{p}^2$ hybridised $B$ atom and is planar. Since this groups are attached with linear shape $-C\equiv C-$ species which makes the whole molecule planar.
(c) $N$ in $N(Si{H}_3{)}_3$ is $s{p}^2$ hybridised and its lone pair is delocalised in empty $p$ orbital of $Si$. So, it has planar shape.
(d) $N{H}_2-N{H}_2$ has $s{p}^3$ hybridised $N$ atoms and is non-planar.