11 Important Concepts Important Concepts 3.Alkono Propertios- 6.Alkane IR- MR- yc6-100-14 2850cT1 7 Degree of Unsaturation-Number of rings 1-10 kcal/m 2.5.16 4000cm Charactetcbeaktorstetehing.bendingand 11 Important Concepts 11 Important Concepts Heatsof Hydrogenation-indicale re 10. ion of A ohols-D s(and other one。 1010 11 Important Concepts 3. Alkene Properties – • Flat, sp2 hybridization • Dipoles possible • Alkenyl hydrogen is relatively acidic. 4. NMR – • Alkenyl hydrogens and carbons appear at low field: • 1H (δ = 4.6 - 5.7 ppm); 13C (δ = 100 -140 ppm) • Jtrans > Jcis; jgeminal very small; Jallylic variable, small. 5. IR – Measures vibration excitation • 1-10 kcal/mol (2.5-16.7 μm; 600-4000 cm-1) • Characteristic peaks for stretching, bending and other vibrational modes • Fingerprint region (<1500 cm-1) 11 Important Concepts 6. Alkane IR – • C-H Stretching: 2840 to 3000 cm-1 • C=C Stretching: 1620 to 1680 cm-1 • Alkenyl C-H Stretching: ~3100 cm-1 • Bending Modes: below 1500 cm-1 • Alcohols: Broad O-H stretch: between 3200 and 3650 cm-1 7. Degree of Unsaturation – Number of rings + number of π bonds: • Degree of unsaturation = (Hsat – Hactual)/2 • Hsat = 2nC + 2 – NX + NN (disregard oxygen and sulfur) 11 Important Concepts 8. Heats of Hydrogenation – indicate relative stability of isomeric alkenes. • Stability decreases with decreasing substitution. • Trans isomers are more stable than cis. 9. Eliminations of Haloalkanes (and other alkyl derivatives) – • Follow the Sayzex rule (non-bulky base, internal alkene formation) or the Hofmann rule (bulky base, terminal alkene formation). • Trans alkene products predominate over cis. • Elimination is stereospecific (dictated by the anti transition state). 11 Important Concepts 10. Dehydration of Alcohols – Dehydration in the presence of strong acid results in a mixture of products (major constituent is the most stable alkene)