Subject: 1,5-Diaminotetrazole aminogroup structure

From: Alexander Kulak <[email-masked]>
Date: Sat, 11 Aug 2001 20:28:54 +0300 (EEST)

Hello, All.

               "N6" ------>  NH2
                             |
                           // \
                           N   N - NH2  <------ "N5"
                           |   |
                           N = N

X-ray investigation of this compound shows that N6 aminogroup
is planar (angles = 118,118,119) and lies in the tetrazole plane.

But MP2/6-31G(d,p) calculation gives the non-planar structure of that
aminogroup (112,113,114 degrees), although H atoms lie close to the ring plane,
in contrast with N5, where they lie at the different sides of the plane.

The HOMO is combined from p(z)-AO of ring's nitrogens and p(z) of N6,
confirming common assumpion about Pi-conjugation of ring and N6.
At the same time localization (Boys or Pipek-Mezey) gives a clear
picture of lone-pair at N6.

Could anyone please answer the QUESTIONS:

1) Why calculated N6 is not planar while nature says it is planar?
2) Why it CAN be planar?

b.w., Alexander Kulak   [ http://i.am/kulak ]