Scalar coupling between nuclei depends on electron density on nucleus CH coupling constant: cyclopropane (165.4 Hz) Annual Review of N.M.R. Spectroscopy By Eric Francis Mooney Hyperconjugation experimental observations – alkyl substitution reduces heat of alkene hydrogenation: 2-trans-hexene (27.3 kcal/mol)/1-hexene (29.7 kcal/mol) same product!! – substitution makes cation formation faster affect attributed to hyperconjugation delocalization of electrons   described as bond-no bond resonance on delocalization precursor to hydride rearrangement – factors that affect bond strength, length, rotation??? (101 kcal/mol) C-C (83 kcal/mol) C=C (143 kcal/mol) OH (110 kcal/mol) C-O (86 kcal/mol C=O (179 kcal/mol) Ketone v. enol? (why?), overlap, hybridization (why?) alkanes staggered and eclipsed conformations – ethane 2.7 kcal/mol barrier 1012 s at room temperature – – – of restricted rotation rings in general review - atomic/molecular properties inductive through bond field effect is through space (cis and trans 1,2-disubstituted cyclopropane). charge/charge > charge/dipole > dipole/dipole orbital overlap mismatch in size, HF (565 KJ/mol) v HI (295 KJ/mol) – –
Scalar coupling between nuclei depends on electron density on nucleus CH coupling constant: cyclopropane (165.4 Hz) Annual Review of N.M.R. Spectroscopy By Eric Francis Mooney Hyperconjugation – experimental observations alkyl substitution reduces heat of alkene hydrogenation: 2-trans-hexene (27.3 kcal/mol)/1-hexene (29.7 kcal/mol) – same product!! substitution makes cation formation faster affect attributed to hyperconjugation  delocalization of  electrons described as bond-no bond resonance on delocalization – precursor to hydride rearrangement factors that affect bond strength, length, rotation??? (101 kcal/mol) C-C (83 kcal/mol) C=C (143 kcal/mol) OH (110 kcal/mol) C-O (86 kcal/mol C=O (179 kcal/mol) Ketone v. enol? (why?), overlap, hybridization (why?) alkanes – staggered and eclipsed conformations – ethane – 2.7 kcal/mol barrier – 1012 s at room temperature of restricted rotation rings in general review - atomic/molecular properties inductive through bond field effect is through space (cis and trans 1,2-disubstituted cyclopropane). charge/charge > charge/dipole > dipole/dipole – orbital overlap – mismatch in size, HF (565 KJ/mol) v HI (295 KJ/mol)