The characterization of NMR shielding in monocyclic phosphines

✍ Scribed by D. B. Chesnut; L. D. Quin; S. B. Wild

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 178 KB
• Volume: 8
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/(sici)1098-1071(1997)8:5<451::aid-hc10>3.0.co;2-q

✦ Synopsis

The phenyl-substituted saturated monocyclic phosphines, PhP(CH 2 ) n , n ‫ס‬ 2-5, show an interesting variation in their phosphorus NMR shieldings. The shielding does not vary uniformly with ring size, but rather the smallest ring (n ‫ס‬ 2) has the highest shielding while the next smallest (n ‫ס‬ 3) has the lowest shielding. Hartree-Fock calculations in the gauge-including atomic orbital (GIAO) approach on the related hydrogen derivatives have reproduced this trend in shielding and allow a qualitative understanding of the experimental observations. With respect to the relatively unstrained n ‫ס‬ 4,5 ring systems, the unusual behavior of the n ‫ס‬ 2 and 3 molecules can be understood in terms of the differences in the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) gaps and the p-character of the phosphorus lone pair. The HOMO/LUMO gap is largest for phosphirane (n ‫ס‬ 2) but smallest in phosphetane (n ‫ס‬ 3). The hybrid character of the lone pair in phosphirane (n ‫ס‬ 2) is almost sp while that for phosphetane (n ‫ס‬ 3) is essentially sp 2 .