8Chapter 04

Wolfs chm 201 202 4 100 example example ch3ch25ch2oh

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: % 4- 99 The SN2 Mechanism The SN2 Mechanism The Two-step mechanism for conversion of alcohols Two-step to alkyl halides: (1) proton transfer to alcohol to form alkyloxonium ion alkyloxonium (2) bimolecular displacement of water (2) from alkyloxonium ion by halide Dr. Wolf's CHM 201 & 202 4- 100 Example Example CH3(CH2)5CH2OH + HBr 120°C CH3(CH2)5CH2Br + H2O Dr. Wolf's CHM 201 & 202 4- 101 Mechanism Mechanism Step 1: Proton transfer from HBr to 1-heptanol Step Proton CH3(CH2)5CH2 CH .. O: + H .. Br: .. H fast, bimolecular H + CH3(CH2)5CH2 O : + .. – : Br: .. H Heptyloxonium ion Dr. Wolf's CHM 201 & 202 4- 102 Mechanism Mechanism Step 2: Reaction of alkyloxonium ion with bromide Step Reaction ion. ion. H .. – + : Br: + CH3(CH2)5CH2 O : .. H slow, bimolecular CH3(CH2)5CH2 .. Br: .. 1-Bromoheptane 1-Bromoheptane Dr. Wolf's CHM 201 & 202 H + :O: H 4- 103 δ– Br δ+ CH2 OH2 CH3(CH2)4CH2 proton transfer ROH Dr. Wolf's CHM 201 & 202 + ROH2 RX 4- 104 4.14 Other Methods for Converting Other Alcohols to Alkyl Halides Alcohols Dr. Wolf's CHM 201 & 202 4- 105 Reagents for ROH to RX Reagents for ROH to RX Thionyl chloride SOCl2 + ROH → RCl + HCl + SO2 Phosphorus tribromide PBr3 + 3ROH → 3RBr + H3PO3 Dr. Wolf's CHM 201 & 202 4- 106 Examples Examples CH3CH(CH2)5CH3 SOCl2 K2CO3 CH3CH(CH2)5CH3 Cl OH (81%) (pyridine often used instead of K2CO3) (CH3)2CHCH2OH PBr3 (CH3)2CHCH2Br (55-60%) Dr. Wolf's CHM 201 & 202 4- 107 4.15 Halogenation of Alkanes RH + X2 → RX + HX Dr. Wolf's CHM 201 & 202 4- 108 Energetics Energetics RH + X2 → RX + HX explosive for F2 exothermic for Cl2 and Br2 endothermic for I2 Dr. Wolf's CHM 201 & 202 4- 109 4.16 Chlorination of Methane Dr. Wolf's CHM 201 & 202 4- 110 Chlorination of Methane Chlorination of Methane carried out at high temperature (400 °C) CH4 + Cl2 → CH3Cl + HCl CH3Cl + Cl2 → CH2Cl2 + HCl CH2Cl2 + Cl2 → CHCl3 + HCl CHCl3 + Cl2 → CCl4 + HCl Dr. Wolf's CHM 201 & 202 4- 111 4.17 Structure and Stability of Free Structure Radicals Radicals Dr. Wolf's CHM 201 & 202 4- 112 Free Radicals Free Radicals contain unpaired electrons .. .. : O O: Examples: O2 . . .. . : N O: NO .. : Cl . Cl .. Dr. Wolf's CHM 201 & 202 4- 113 Alkyl Radicals Alkyl Radicals R . C R R Most free radicals in which carbon bears the unpaired electron are too unstable to be isolated. Alkyl radicals are classified as primary, secondary, or tertiary in the same way that carbocations are. Dr. Wolf's CHM 201 & 202 4- 114 Figure 4.19 Structure of methyl radical. Figure 4.19 Structure of methyl radical. Methyl radical is planar, which suggests that Methyl carbon is sp2 hybridized and that the unpaired sp electron is in a p orbital. orbital. Dr. Wolf's CHM 201 & 202 4- 115 Alkyl Radicals Alkyl Radicals R . C R R The order of stability of free radicals is the The same as for carbocations. same Dr. Wolf's CHM 201 & 202 4- 116 Alkyl Radicals Alkyl Radicals H . C H3C H less stable than H Methyl radical H3C less stable than . C CH3 H Isopropyl radical Dr. Wolf's CHM 201 & 202 (secondary) . C H H Ethyl radical (primary) H3C less stable than . C CH3 CH3 tert-Butyl radical (tertiary)4- 117 Alkyl Radicals Alkyl Radicals The order of stability of free radicals can The be determined by measuring bond strengths. By "bond strength" we mean the energy required to break a cov...
View Full Document

Ask a homework question - tutors are online