Q3. In a quaternary ammonium ion, R4N+, is the nitrogen still pyramidal?
No. Its unshared pair has been used to form a fourth bond, so all four sp3 orbitals hold bonds and the four groups sit at the corners of a tetrahedron (reasoned from NCERT pages 259 and 262).
Q4. What do NCERT’s words “secondary amino group” in adrenaline and ephedrine tell you about the nitrogen in them?
The nitrogen carries two carbon groups and one hydrogen, –NH–, and, in the neutral form, an unshared electron pair (reasoned from NCERT pages 259–260).
Q5. The measured angles are 110.9° for C–N–C in trimethylamine and 106.7° for H–N–H in ammonia. How many degrees wider is the trimethylamine angle, and which of the two is smaller than the tetrahedral 109.5°?
110.9 − 106.7 = 4.2° wider. Only ammonia’s 106.7° is smaller than 109.5°; trimethylamine’s measured angle is larger (reasoned from the NIST data).
Q6. Name the orbital that holds nitrogen’s unshared pair in the simple alkylamine model and the shape of the molecule around nitrogen.
The fourth sp3 hybrid orbital of nitrogen; the shape around nitrogen is pyramidal (NCERT page 259).