Nature and Strength of the .lambda.5-P:C "Double" Bond

Abstract

The strength of the "second bond" in H3P=CH2 has been obtained in different ways at the MP4/6-3 1 1G**/ /MP2/6-31 lG**+ZPE level of theory. The calculated bond strengths of 33.7 and 38.4 k c d m o l are comparable to those obtained for the A3-P=C bond (38-49 kcaymol). The similarity in bond strengths could explain the similar bond lengths of the two systems. The rotational barrier about the P-C bond in H3P=CH2 obtained at the QCISD/6-31 I+G**+ZPE level of theory is 0.9 kcaymol. The low barrier is, however, not necessarily an indication of a weak double bond but is probably the consequence of the similar bond strength of the "second bond" for both rotational conformers. The bonding MO-model evaluated here for the description of the less stable conformer can be derived from the n-MO of the A3-P=C bond; the resulting electronic structure is similar to an allylic n-system. Topological electron density analysis has indeed shown that the electron density and ellipticity at the bond critical point of the somewhat less stable conformer can be related to those of HP=CH;, and similarly to those of allyl ion and ethane.

An electron localization function investigation of bonding in some simple four‐coordinate nitrogen and phosphorus compounds

“…Nyulá szi et al [13] have presented arguments that the multiple bond in H 3 PCH 2 has many similarities to the conventional multiple bond in HPCH 2 .…”

Synthesis of an Imidazolium Phosphanide Zwitterion and Its Conversion into Anionic Imidazol‐2‐ylidene Derivatives

“…The same holds true for other ylidic compounds, such as II, the deoxy-Breslow intermediate III, [27,28] and methylene-phosphorane H 3 P= CH 2. [29] Further calculations (at different levels of theory, see the Supporting Information) on the isomeric structures revealed that II is the most stable structure for the parent system (R 1 , R 2 , R 3 = H), while V and IV are less stable by 16.6 and 18.6 kcal mol À1 , respectively, and VI is even more destabilized (34.8 kcal mol À1 less stable than II; Scheme 4).…”

Aromaticity and Antiaromaticity of Four-Membered P-Heterocycles

“…Energies of isodesmic reactions and -ionization revealed that energy gain is nearly the same for 3 -P=C and C=C bonded system [48,49], therefore the statement that the 3 -P atom is a "carbon copy" is many times correct [36]. However, the 5 -P=C system can rather be characterized as a state between the zwitter-ionic and the genuine double bond system [50][51][52].…”