Lecture 13

Lecture 13 - Carbenes Carey & Sundberg, Part B, Chapter...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Carbenes Carey & Sundberg , Part B, Chapter 10, 614-650.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
H H H H Carbene Electronic Structure Triplet (two unpaired e - ) Singlet (all e - paired) p σ σ p Often has radica l-like character Capale of both electrophilic and nucleophilic behavior 1.078 Å 133.8˚ Nitrene Electronic Structure R N Singlet (all e - paired) empty filled R N H Nitrenium ion H Carbenes: Introduction
Background image of page 2
p E n e r g y σ Due to electron repulsion, there is an energy cost in pairing both electrons in the σ orbital. If a small energy difference between the σ and p orbitals exists, the electrons will remain unpaired (triplet) . If a large gap exists between the σ and p orbitals the electrons will pair in the σ orbital ( singlet ). singlet 8–10 kcal/mol T 1 S 1 Carbene Configuration: Triplet vs. Singlet p σ triplet The History of the Singlet-Triplet Gap Method HCH Angle S–T Splitting kcal/mol Author Year Qual. 90-100° –– Muliken 1932 Grnd State singlet Thermochem 180° small Walsh 1947 triplet 160° 30 Gallup 1957 Qual. QM 138° >33 Harrison 1969 Ab initio –– 8–9 Hase 1971 Kinetics 19 Pople 1971 SCF 132° 8.7 Dewar 1974 MINDO 134° 19.5 Lineberger 1976 Expt 138° 19.7 Schaeffer 1976 An Initio ––– 8.1 Zare 1978 Expt ––– 8.5 Haydon 1982 Expt ––– Carbenes: Introduction
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The p orbital of carbenes substituted with p-donor atoms (N, O, halogen) is raised high enough in energy to make the pairing of the electrons in the σ orbital energetically favorable. As a result, these carbenes are often in the singlet state. C Cl Cl Heteroatom-Substituted Carbenes: Singlets p triplet carbene σ Energy donor p orbital π -donor heteroatom Heteroatom- substituted carbene Examples: Singlet C H C 6 H 5 Singlet Carbene Structure
Background image of page 4
C X X X H C Cl Cl C C O R R Alkyl Halides
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/09/2010 for the course CH CH242 taught by Professor Katz during the Spring '10 term at Colby.

Page1 / 20

Lecture 13 - Carbenes Carey & Sundberg, Part B, Chapter...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online