The previous posts have seen how a molecule containing a hypervalent carbon atom can be designed by making a series of logical chemical connections. Another logical step is to investigate whether the adjacent atoms in the periodic table may exhibit similar effects (C2+ ≡ B+ ≡ N3+ ≡ Be ≡ O4+). So here are reported some results (B3LYP/6-311G(d,p) ) for boron, beryllium and nitrogen, for the general tetramethyl substituted system shown below
Pentavalency across a series
| X | Charge | X-C length, Å | ρ(r) C-X | ELF integration | ν-Trampoline, cm-1 | ν X-H, cm-1 | Repository |
| N | 2 | 1.616 | .172 | 1.14 | 883 | 3417 | 10042/to-2439 |
| C | 1 | 1.580 | .195 | 1.10 | 970 | 3291 | 10042/to-2438 |
| B | 0 | 1.649 | .136 | 1.06 | 949 | 2746 | 10042/to-2440 |
| Be | -1 | 1.817 | .064 | 0.98 | 797 | 1887 | 10042/to-2441 |
The systems H, C and B are stable in the sense that the C4v-symmetric calculated geometry has only positive calculated force constants (Be has a small negative frequency). All show bond critical points in the X-C region (although these bonds are clearly bent) and X-H region, and significant integrations for the X-C disynaptic basins in the ELF analysis. The boron analogue is also of interest as being a neutral rather than a charged molecule, and therefore may be a worthy target for synthetic effort.
Tags: Hypervalency, Interesting chemistry, logical chemical connections