8Chapter 04

Fluorine dr wolfs chm 201 202 4 45 solubility in

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Unformatted text preview: olarizable and induced dipoleiinduced dipole forces decrease with increasing nduced fluorine substitution. fluorine Dr. Wolf's CHM 201 & 202 4- 45 Solubility in water Solubility in water Alkyl halides are insoluble in water. Methanol, ethanol, isopropyl alcohol are completely miscible with water. The solubility of an alcohol in water decreases with increasing number of decreases carbons (compound becomes carbons more hydrocarbon-like). Dr. Wolf's CHM 201 & 202 4- 46 Figure 4.5 Hydrogen Bonding Figure 4.5 Hydrogen Bonding Figure Figure Between Ethanol and Water Between Ethanol and Water Between Between δ+ δ– δ+ δ+ δ– δ– Dr. Wolf's CHM 201 & 202 4- 47 Density Density Alkyl fluorides and alkyl chlorides are less dense than water. Alkyl bromides and alkyl iodides are Alkyl more dense than water. more All liquid alcohols have densities of All about 0.8 g/mL. about Dr. Wolf's CHM 201 & 202 4- 48 4.7 Preparation of Alkyl Halides from Alcohols and Hydrogen Halides ROH + HX → RX + H2O ROH Dr. Wolf's CHM 201 & 202 4- 49 Reaction of Alcohols with Hydrogen Halides Reaction of Alcohols with Hydrogen Halides ROH + HX → RX + HOH Hydrogen halide reactivity HF least reactive least Dr. Wolf's CHM 201 & 202 HCl HBr HI most reactive 4- 50 Reaction of Alcohols with Hydrogen Halides Reaction of Alcohols with Hydrogen Halides ROH + HX → RX + HOH Alcohol reactivity CH3OH Methanol RCH2OH R2CHOH Primary Secondary least reactive least Dr. Wolf's CHM 201 & 202 R3COH Tertiary most reactive 4- 51 Preparation of Alkyl Halides Preparation of Alkyl Halides 25°C (CH3)3COH + HCl (CH3)3CCl + H2O 78-88% OH + HBr OH 80-100°C Br + H2O Br 73% CH3(CH2)5CH2OH + HBr 120°C CH3(CH2)5CH2Br + H2O Dr. Wolf's CHM 201 & 202 87-90% 4- 52 Preparation of Alkyl Halides Preparation of Alkyl Halides A mixture of sodium bromide and sulfuric mixture acid may be used in place of HBr. acid CH3CH2CH2CH2OH Dr. Wolf's CHM 201 & 202 NaBr H2SO4 heat CH3CH2CH2CH2Br 70-83% 4- 53 4.8 Mechanism of the Reaction of Mechanism Alcohols with Hydrogen Halides Alcohols Dr. Wolf's CHM 201 & 202 4- 54 About mechanisms About mechanisms A mechanism describes how reactants are converted to products. Mechanisms are often written as a series of chemical equations showing the elementary chemical steps. steps. An elementary step is a reaction that proceeds by way of a single transition state. Mechanisms can be shown likely to be correct, Mechanisms likely but cannot be proven correct. but proven Dr. Wolf's CHM 201 & 202 4- 55 About mechanisms About mechanisms For the reaction: (CH3)3COH + HCl tert-Butyl alcohol 25°C (CH3)3CCl + H2O tert-Butyl chloride the generally accepted mechanism involves the three elementary steps. Step 1 is a Brønsted acid-base reaction. Step Dr. Wolf's CHM 201 & 202 4- 56 Like proton transfer Step 1: Proton transfer Step 1: Proton transfer from a strong acid to water, proton transfer .. .. (CH3)3C O : + H Cl: from a strong acid to .. an alcohol is normally H very fast. very fast fast, bimolecular fast, H + (CH3)3C O : + .. – : Cl: .. H tert-Butyloxonium ion Dr. Wolf's CHM 201 & 202 4- 57 Step 1: Proton transfer Step 1: Proton transfer (CH3)3C .. O: + H .. Cl: .. H Two molecules react in this elementary step; therefore it is step; bimolecular. bimolecular fast, bimolecular fast, H + (CH3)3C O : + .. – : Cl: ....
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This document was uploaded on 01/03/2012.

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