Question

Give reasons for the following:
$R_{3}P=O$ exists but $R_{3}N=O$ does not, $R$ is an alkyl group?

Answer 1

Nitrogen cannot have covalency more than 4. This is the restriction which comes in nitrogen(N) to expand its coordination number beyond four. Hence, $R_{3}N=O$ does not exist. But P can show covalency of 5. Hence, $R_{3}P=O$ exists.

Nitrogen cannot form $d\pi -p\pi$ bonds but phosphorous can form $d\pi -p\pi$ bonds.