Q

# Why does R3P = O exist but R3N = O does not (R = alkyl group)?

7.10     Why does $R_{3}P=0$ exist but $R_{3}N=0$  does not $(R = alkyl\: group)$?

$N$ does not have any $d$-orbitals but phosphorus($P$) does. This is the restriction which comes in nitrogen($N$) to expand its coordination number beyond four. Hence, $R_3N=O$ does not exist.