《有机化学》课程教学资源（教材文献，英文版）CHAPTER 4 ALCOHOLS AND ALKYL HALIDES

CHAPTER 4 ALCOHOLS AND ALKYL HALIDES SOLUTIONS TO TEXT PROBLEMS 4.1 There are four C4H, alkyl groups, and so there are four C4HOCI alkyl chlorides. Each may be named by both the functional class and substitutive methods. The functional class name uses the name of the alkyl group followed by the halide as a second word. The substitutive name modifies the name of the corresponding alkane to show the location of the halogen atom. nctional class name ve name CH, CH, CH, CH,CI n-Butyl chloride 1-Chlorobutane (Butyl chloride) CHaCHCH, CH3 sec-Butyl chloride 2-Chlorobutane (1-Methylpropyl chloride) CH, CHCH,CI Isobutyl chloride 1-Chloro-2-methylpropane (2-Methylpropyl chloride) CH3CCH tert-Butyl chloride 2-Chloro-2-methylpropane (1, 1-Dimethylethyl chloride) 4.2 Alcohols may also be named using both the functional class and substitutive methods, as in the 67 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

67 CHAPTER 4 ALCOHOLS AND ALKYL HALIDES SOLUTIONS TO TEXT PROBLEMS 4.1 There are four C4H9 alkyl groups, and so there are four C4H9Cl alkyl chlorides. Each may be named by both the functional class and substitutive methods. The functional class name uses the name of the alkyl group followed by the halide as a second word. The substitutive name modifies the name of the corresponding alkane to show the location of the halogen atom. Functional class name Substitutive name CH3CH2CH2CH2Cl n-Butyl chloride 1-Chlorobutane (Butyl chloride) sec-Butyl chloride 2-Chlorobutane (1-Methylpropyl chloride) Isobutyl chloride 1-Chloro-2-methylpropane (2-Methylpropyl chloride) tert-Butyl chloride 2-Chloro-2-methylpropane (1,1-Dimethylethyl chloride) 4.2 Alcohols may also be named using both the functional class and substitutive methods, as in the previous problem. CH3CHCH2CH3 Cl CH3CHCH2Cl CH3 CH3 CH3CCH3 Cl Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

68 ALCOHOLS AND ALKYL HALIDES Functional class name bstitutive name CHCH, CH,CH,OH n-Butyl alcohol 1-Butanol CH3 CHCH, CH3 sec-Butyl alcohol 2-Butanol (l-Methylpropyl alcohol) CH3 CHCH,OH Isobutyl alcohol 2-Methyl-1-propanol (2-Methylpropyl alcohol) CH CCH tert-Butyl alcohol 2-Methyl-2-propanol (1, I-Dimethylethyl alcohol) 4.3 Alcohols are classified as primary, secondary, or tertiary according to the number of carbon substituents attached to the carbon that bears the hydroxyl group. H..CH CH3C—CH2CH3 Primary alcohol econdary alcohol (one alkyl group bonded to--CH, OH) (two alkyl groups bonded to/CHOH) CH (CH3)2CH—C-OH CH -C-OH Primary kyl group bonded to-CH, OH)(three alkyl groups bonded to - COH) 4.4 Dipole moment is the product of charge and distance. Although the electron distribution in the carbon-chlorine bond is more polarized than that in the carbon-bromine bond, this effect is counterbalanced by the longer carbon-bromine bond distance Distance Charge CH -CI CH--Br Methyl chloride (greater value of e) 8D 4.5 All the hydrogens in dimethyl ether(CH3OCH3) are bonded to carbon; therefore, intermolecular hydrogen bonding between dimethyl ether molecules does not take place, and its boiling point is lower than that of ethanol (CHa CH,OH), where hydrogen bonding involving the -OH group is 4.6 Ammonia is a base and abstracts(accepts)a proton from the acid (proton donor) hydrogen chloride H3N NH, cl: B Acid Conjugate Conjugate Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

68 ALCOHOLS AND ALKYL HALIDES Functional class name Substitutive name CH3CH2CH2CH2OH n-Butyl alcohol 1-Butanol (Butyl alcohol) sec-Butyl alcohol 2-Butanol (1-Methylpropyl alcohol) Isobutyl alcohol 2-Methyl-1-propanol (2-Methylpropyl alcohol) tert-Butyl alcohol 2-Methyl-2-propanol (1,1-Dimethylethyl alcohol) 4.3 Alcohols are classified as primary, secondary, or tertiary according to the number of carbon substituents attached to the carbon that bears the hydroxyl group. 4.4 Dipole moment is the product of charge and distance. Although the electron distribution in the carbon–chlorine bond is more polarized than that in the carbon–bromine bond, this effect is counterbalanced by the longer carbon–bromine bond distance. 4.5 All the hydrogens in dimethyl ether (CH3OCH3) are bonded to carbon; therefore, intermolecular hydrogen bonding between dimethyl ether molecules does not take place, and its boiling point is lower than that of ethanol (CH3CH2OH), where hydrogen bonding involving the @OH group is important. 4.6 Ammonia is a base and abstracts (accepts) a proton from the acid (proton donor) hydrogen chloride. H Cl 3N H NH4 Cl Base Acid Conjugate acid Conjugate base  e  d Charge Dipole moment Distance CH3 Cl Methyl chloride (greater value of e) 1.9 D CH3 Br Methyl bromide (greater value of d) 1.8 D (CH3)2CH C H H OH Primary alcohol (one alkyl group bonded to CH2OH) CH3 CH3 CH3 C OH Tertiary alcohol (three alkyl groups bonded to COH) CH3CH2CH2 C H H OH Primary alcohol (one alkyl group bonded to CH2OH) CH3 C OH H CH2CH3 Secondary alcohol (two alkyl groups bonded to CHOH) CH3CHCH2CH3 OH CH3CHCH2OH CH3 CH3 CH3CCH3 OH Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

ALCOHOLS AND ALKYL HALIDES 69 4.7 Since the pk, of HCN is given as 9.1, its K=10.. In more conventional notation, K 8X10. Hydrogen cyanide is a weak acid 4.8 Hydrogen cyanide is a weak acid, but it is a stronger acid than water(pK= 15.7). Since HCN is a stronger acid than water, its conjugate base(Cn )is a weaker base than hydroxide(Ho), which the conjugate base of water. 4.9 An unshared electron pair on oxygen abstracts the proton from hydrogen chloride CHD),C. co +HC Co-H + :C: B Acid Conjugate 4.10 In any proton-transfer process, the position of equilibrium favors formation of the weaker acid and the weaker base from the stronger acid and base. Alkyloxonium ions(ROH, t) have approximately the same acidity as hydronium ion(H,o, pk=-1.7). Thus hydrogen chloride(pK,"-7)is the stronger acid. tert-Butyl alcohol is the stronger base because it is the conjugate of the weaker acid (tert-butyloxonium ion) (CH3)3COH HCI (CH3)3COH2 CI The equilibrium constant for proton transfer from hydrogen chloride to tert-butyl alcohol is much greater than 1 4.11 The proton being transferred is partially bonded to the oxygen of tert-butyl alcohol and to chloride at the transition state 8-+-c 4.12 (b) Hydrogen chloride converts tertiary alcohols to tertiary alkyl chlorides (CH,CH,)COH (CH,CH2)3CCI H,O 3-Ethyl-3-pentanol 3-Chloro-3-ethylpentane (c) 1-Tetradecanol is a primary alcohol having an unbranched 14-carbon chain. Hydrogen bromide reacts with primary alcohols to give the corresponding primary alkyl bromide CHa(CH2)12CH,OH HBr CHa(CH)) CH,Br H,O Hydrogen 4.13 The order of carbocation stability is tertiary secondary primary. There is only one CsH,car- bocation that is tertiary, and so that is the most stable one. CH3,C+ 1, 1-Dimethylpropyl cation Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

4.7 Since the pKa of HCN is given as 9.1, its Ka  109.1. In more conventional notation, Ka  8  1010. Hydrogen cyanide is a weak acid. 4.8 Hydrogen cyanide is a weak acid, but it is a stronger acid than water (pKa  15.7). Since HCN is a stronger acid than water, its conjugate base (CN) is a weaker base than hydroxide (HO), which is the conjugate base of water. 4.9 An unshared electron pair on oxygen abstracts the proton from hydrogen chloride. 4.10 In any proton-transfer process, the position of equilibrium favors formation of the weaker acid and the weaker base from the stronger acid and base. Alkyloxonium ions (ROH2 ) have approximately the same acidity as hydronium ion (H3O, pKa  1.7). Thus hydrogen chloride (pKa 7) is the stronger acid. tert-Butyl alcohol is the stronger base because it is the conjugate of the weaker acid (tert-butyloxonium ion). The equilibrium constant for proton transfer from hydrogen chloride to tert-butyl alcohol is much greater than 1. 4.11 The proton being transferred is partially bonded to the oxygen of tert-butyl alcohol and to chloride at the transition state. 4.12 (b) Hydrogen chloride converts tertiary alcohols to tertiary alkyl chlorides. (c) 1-Tetradecanol is a primary alcohol having an unbranched 14-carbon chain. Hydrogen bromide reacts with primary alcohols to give the corresponding primary alkyl bromide. 4.13 The order of carbocation stability is tertiary  secondary  primary. There is only one C5H11 car￾bocation that is tertiary, and so that is the most stable one. 1,1-Dimethylpropyl cation CH3CH2C CH3 CH3 CH3(CH2)12CH2OH HBr 1-Tetradecanol CH3(CH2)12CH2Br Hydrogen 1-Bromotetradecane bromide H2O Water (CH3CH2)3COH HCl 3-Ethyl-3-pentanol (CH3CH2)3CCl Hydrogen 3-Chloro-3-ethylpentane chloride H2O Water O H Cl H (CH3)3C (CH3)3COH HCl Cl Stronger base (pKa 7) Stronger acid (CH3)3COH2 (pKa 1.7) Weaker acid Weaker base Acid H Cl H Conjugate base Cl Conjugate acid O (CH3)3C H Base O (CH3)3C H ALCOHOLS AND ALKYL HALIDES 69 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

ALCOHOLS AND ALKYL HALIDES 4.14 1-Butanol is a primary alcohol; 2-butanol is a secondary alcohol. A carbocation intermediate is possible in the reaction of 2-butanol with hydrogen bromide but not in the corresponding reaction of 1-butanol The mechanism of the reaction of 1-butanol with hydrogen bromide proceeds by displacement of water by bromide ion from the protonated form of the alcohol(the alkyloxonium ion) Protonation of the alcohol CH CH, CH,CH,O:+ H →CH2CH CHO++ Hydroge Bromide Displacement of water by bromide: CHCHCH CH,O+ CH CH Br o The slow step, displacement of water by bromide from the oxonium ion, is bimolecular. The reaction of 1-butanol with hydrogen bromide follows the Sn2 mechanism. The reaction of 2-butanol with hydrogen bromide involves a carbocation intermediate Protonation of the alcohol CH3 CH CHCH3+ CH3,CHCH3 Br: 2-Butanol sec-Butyloxonium ion Bromide io Dissociation of the oxonium ion CH3, CHCH3 CHaCH,CHCH Butyloxonium io sec-Butyl cation Water Capture of sec-butyl cation by bromide: CHCH Br CHCH2—CH3CH2CHCH3 Bromide ion sec-Butyl cation 2-Bromobutane The slow step, dissociation of the oxonium ion, is unimolecular. The reaction of 2-butanol with 4.15 The most stable alkyl free radicals are tertiary. The tertiary free radical having the formula C has the same skeleton as the carbocation in Problem 4.13 CH CH CH2-C Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

4.14 1-Butanol is a primary alcohol; 2-butanol is a secondary alcohol. A carbocation intermediate is possible in the reaction of 2-butanol with hydrogen bromide but not in the corresponding reaction of 1-butanol. The mechanism of the reaction of 1-butanol with hydrogen bromide proceeds by displacement of water by bromide ion from the protonated form of the alcohol (the alkyloxonium ion). Protonation of the alcohol: Displacement of water by bromide: The slow step, displacement of water by bromide from the oxonium ion, is bimolecular. The reaction of 1-butanol with hydrogen bromide follows the SN2 mechanism. The reaction of 2-butanol with hydrogen bromide involves a carbocation intermediate. Protonation of the alcohol: Dissociation of the oxonium ion: Capture of sec-butyl cation by bromide: The slow step, dissociation of the oxonium ion, is unimolecular. The reaction of 2-butanol with hydrogen bromide follows the SN1 mechanism. 4.15 The most stable alkyl free radicals are tertiary. The tertiary free radical having the formula C5H11 has the same skeleton as the carbocation in Problem 4.13. CH3CH2 C CH3 CH3 Bromide ion sec-Butyl cation 2-Bromobutane CH3CH2CHCH3 Br CHCH3 CH3CH2 Br CH3CH2CHCH3 O H H CH3CH2CHCH3 O H H sec-Butyloxonium ion sec-Butyl cation Water slow CH3CH2CHCH3 O H Br 2-Butanol Hydrogen bromide sec-Butyloxonium ion Bromide ion H Br CH3CH2CHCH3 O H H CH3CH2CH2CH2Br 1-Bromobutane O Water slow Br Bromide ion CH3CH2CH2 CH2 O Butyloxonium ion H H H H CH3CH2CH2CH2O H 1-Butanol H Br Hydrogen bromide Br Butyloxonium ion Bromide CH3CH2CH2CH2O H H 70 ALCOHOLS AND ALKYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

ALCOHOLS AND ALKYL HALIDES 4.16(b riting the equations for carbon-carbon bond cleavage in propane and in 2-methylpropane a primary ethyl radical is produced by a cleavage of propane wh of 2-methylprop CH,CHO -CH3 CHa CH2 CHCHCH CH3 CHCH3 . CH 2-Methylpropane Isopropyl radical Methyl radical A secondary radical is more stable than a primary one, and so carbon-carbon bond cleavage of 2-methylpropane requires less energy than carbon-carbon bond cleavage of propa (c) Carbon-carbon bond cleavage of 2, 2-dimethylpropane gives a tertiary radical / CH CH3 CH CCH3 CH- H CH 2, 2-Dimethylpropane tert-Butyl radical Methyl radical As noted in part(b), a secondary radical is produced on carbon-carbon bond cleavage of 2-methylpropane. We therefore expect a lower carbon-carbon bond dissociation energy for .2-dimethylpropane than for 2-methylpropane, since a tertiary radical is more stable than a 4.17 First write the equation for the overall reaction CHC Chloromethane Chlorine The initiation step is dissociation of chlorine to two chlorine atoms Chlorine 2 Chlorine atoms A chlorine atom abstracts a hydrogen atom from chloromethane in the first propagation step Cl—C.+ H H Chloromethane Chlorine atom Chloromethyl radical Hydrogen ch Chloromethyl radical reacts with Cl, in the next propagation step H g!1g:一Cl-C-g: nloromethyl radical Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

4.16 (b) Writing the equations for carbon–carbon bond cleavage in propane and in 2-methylpropane, we see that a primary ethyl radical is produced by a cleavage of propane whereas a secondary isopropyl radical is produced by cleavage of 2-methylpropane. A secondary radical is more stable than a primary one, and so carbon–carbon bond cleavage of 2-methylpropane requires less energy than carbon–carbon bond cleavage of propane. (c) Carbon–carbon bond cleavage of 2,2-dimethylpropane gives a tertiary radical. As noted in part (b), a secondary radical is produced on carbon–carbon bond cleavage of 2-methylpropane. We therefore expect a lower carbon–carbon bond dissociation energy for 2,2-dimethylpropane than for 2-methylpropane, since a tertiary radical is more stable than a secondary one. 4.17 First write the equation for the overall reaction. The initiation step is dissociation of chlorine to two chlorine atoms. A chlorine atom abstracts a hydrogen atom from chloromethane in the first propagation step. Chloromethyl radical reacts with Cl2 in the next propagation step. Chlorine Cl Dichloromethane Chlorine atom C Cl H H C Cl Cl Cl H H Cl Chloromethyl radical Cl Chlorine atom H Cl Chloromethyl radical Hydrogen chloride C H H Cl H C H H Cl Chloromethane Cl Chlorine 2 Chlorine atoms Cl Cl Cl CH3Cl Cl 2 Chloromethane CH2Cl2 Chlorine Dichloromethane HCl Hydrogen chloride CH3CCH3 CH3 CH3 CH3 CH3 C CH3 2,2-Dimethylpropane tert-Butyl radical Methyl radical CH3 CH3CH2 CH3 CH3CH2 CH3 Propane Ethyl radical Methyl radical CH3CHCH3 CH3CHCH3 CH3 2-Methylpropane Isopropyl radical Methyl radical CH3 ALCOHOLS AND ALKYL HALIDES 71 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

ALCOHOLS AND ALKYL HALIDES 4.18 Writing the structural formula for ethyl chloride reveals that there are two nonequivalent sets of hydrogen atoms, in either of which a hydrogen is capable of being replaced by chlorine CHCHCI CH, CICH, CH,CI Ethyl chloride L. 1-Dichloroethane The two dichlorides are 1.1-dichloroethane and 1. 2-dichloroethane. 4.19 Propane has six primary hydrogens and two secondary. In the chlorination of propane, the relative proportions of hydrogen atom removal are given by the product of the statistical distribution and the relative rate per hydrogen. Given that a secondary hydrogen is abstracted 3.9 times faster than a pri mary one, we write the expression for the amount of chlorination at the primary relative to that at the Number of primary hydrogens X rate of abstraction of primary hydrog 6×10.77 Number of secondary hydrogens X rate of abstraction of a secondary hydrogen 2 X 3.9 1.00 Thus, the percentage of propyl chloride formed is 0.77/1.77, or 43%, and that of isopropyl chloride is 57%. (The amounts actually observed are propyl 45%, isopropyl 55%0.) 4.20(b) In contrast with free-radical chlorination, alkane bromination is a highly selective process The major organic product will be the alkyl bromide formed by substitution of a tertiary hydrogen with a b omine Br CH(CH3)2 C(CH3), Tertiary Br 1-lsopropy l-1 1-(1-Bromo-1-methylethyl)- (c) As in part(b), bromination results in substitution of a tertiary hydrogen CH CCH, CHCH CHCCHCCH 2, 2, 4-Trimethylpentane 4.21 (a) Cyclobutanol has a hydroxyl group attached to a four-membered ring (b) sec-Butyl alcohol is the functional class name for 2-butanol CH3 CHCH2 CH3 OH sec-Butyl alcohol (c) The hydroxyl group is at C-3 of an unbranched seven-carbon chain in 3-heptanol CH3 CH, CHCH, CHL CH2CH3 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

4.18 Writing the structural formula for ethyl chloride reveals that there are two nonequivalent sets of hydrogen atoms, in either of which a hydrogen is capable of being replaced by chlorine. The two dichlorides are 1,1-dichloroethane and 1,2-dichloroethane. 4.19 Propane has six primary hydrogens and two secondary. In the chlorination of propane, the relative proportions of hydrogen atom removal are given by the product of the statistical distribution and the relative rate per hydrogen. Given that a secondary hydrogen is abstracted 3.9 times faster than a pri￾mary one, we write the expression for the amount of chlorination at the primary relative to that at the secondary position as:   Thus, the percentage of propyl chloride formed is 0.771.77, or 43%, and that of isopropyl chloride is 57%. (The amounts actually observed are propyl 45%, isopropyl 55%.) 4.20 (b) In contrast with free-radical chlorination, alkane bromination is a highly selective process. The major organic product will be the alkyl bromide formed by substitution of a tertiary hydrogen with a bromine. (c) As in part (b), bromination results in substitution of a tertiary hydrogen. 4.21 (a) Cyclobutanol has a hydroxyl group attached to a four-membered ring. (b) sec-Butyl alcohol is the functional class name for 2-butanol. (c) The hydroxyl group is at C-3 of an unbranched seven-carbon chain in 3-heptanol. OH CH3CH2CHCH2CH2CH2CH3 3-Heptanol OH CH3CHCH2CH3 sec-Butyl alcohol OH Cyclobutanol CH3CCH2CHCH3 2,2,4-Trimethylpentane 2-Bromo-2,4,4-trimethylpentane light Br2 CH3 CH3 CH3 CH3CCH2CCH3 CH3 CH3 CH3 Br CH(CH3)2 CH3 C(CH3)2 CH3 Br Tertiary hydrogen Br2 light 1-(1-Bromo-1-methylethyl)- 1-methylcyclopentane 1-Isopropyl-1- methylcyclopentane 0.77 1.00  6  1 2  3.9  Number of primary hydrogens  rate of abstraction of primary hydrogen Number of secondary hydrogens  rate of abstraction of a secondary hydrogen CH3CH2Cl Ethyl chloride CH3CHCl2 1,1-Dichloroethane 1,2-Dichloroethane ClCH2CH2Cl light or heat Cl2 72 ALCOHOLS AND ALKYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

ALCOHOLS AND ALKYL HALIDES (d) a chlorine at C-2 is on the opposite side of the ring from the C-l hydroxyl group in trans 2-chlorocyclopentanol. Note that it is not necessary to assign a number to the carbon that bears th requires the hydroxyl group to be located at C-1 (e) This compound is an alcohol in which the longest continuous chain that incorporates the hydroxyl function has eight carbons. It bears chlorine substituents at C-2 and C-6 and methyl and hydroxyl groups at C-4 CH3 CH,CHCH,CCH,CHCH, CH3 OH CI (f) The hydroxyl group is at C-1 in trans-4-tert-butylcyclohexanol; the tert-butyl group is at C-4. The structures of the compound can be represented as shown at the left; the structure at the right depicts it in its most stable conformation 3)C (CH)3C trans-4-fert-Butylcyclohexanol (g) The cyclopropyl group is on the same carbon as the hydroxyl group in 1-cyclopropylethanol ch) The cyclopropyl group and the hydroxyl group are on adjacent carbons in 2-cyclopro- CH..OH 4.22(a) This compound has a five-carbon chain that bears a methyl substituent and a bromine. The numbering scheme that gives the lower number to the substituent closest to the end of the chain is chosen. Bromine is therefore at C-l, and methyl is a substituent at C-4 CH CHCH, CH, CH, Br Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

(d) A chlorine at C-2 is on the opposite side of the ring from the C-1 hydroxyl group in trans- 2-chlorocyclopentanol. Note that it is not necessary to assign a number to the carbon that bears the hydroxyl group; naming the compound as a derivative of cyclopentanol automatically requires the hydroxyl group to be located at C-1. (e) This compound is an alcohol in which the longest continuous chain that incorporates the hydroxyl function has eight carbons. It bears chlorine substituents at C-2 and C-6 and methyl and hydroxyl groups at C-4. ( f ) The hydroxyl group is at C-1 in trans-4-tert-butylcyclohexanol; the tert-butyl group is at C-4. The structures of the compound can be represented as shown at the left; the structure at the right depicts it in its most stable conformation. (g) The cyclopropyl group is on the same carbon as the hydroxyl group in 1-cyclopropylethanol. (h) The cyclopropyl group and the hydroxyl group are on adjacent carbons in 2-cyclopro￾pylethanol. 4.22 (a) This compound has a five-carbon chain that bears a methyl substituent and a bromine. The numbering scheme that gives the lower number to the substituent closest to the end of the chain is chosen. Bromine is therefore at C-1, and methyl is a substituent at C-4. CH3 CH3CHCH2CH2CH2Br 1-Bromo-4-methylpentane CH2CH2OH 2-Cyclopropylethanol CHOH CH3 1-Cyclopropylethanol trans-4-tert-Butylcyclohexanol (CH3)3C OH (CH3)3C H H OH 2,6-Dichloro-4-methyl-4-octanol OH CH3CHCH2CCH2CHCH2CH3 Cl Cl CH3 OH Cl trans-2-Chlorocyclopentanol ALCOHOLS AND ALKYL HALIDES 73 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

74 ALCOHOLS AND ALKYL HALIDES (b) This compound has the same carbon skeleton as the compound in part (a) but bears a hydroxyl group in place of the bromine and so is named as a derivative of l-pentanol CH CHCH,CHCH,OH (c) This molecule is a derivative of ethane and bears three chlorines and one bromine The name 2-bromo-l, 1, I-trichloroethane gives a lower number at the first point of difference than 1-bromo-2. 2.2-trichloroethane. ClCCH, Br 2-Bromo.1.1.1-trichloroethane (d) This compound is a constitutional isomer of the preceding one. Regardless of which carbon the numbering begins at, the substitution pattern is 1, 1, 2, 2. Alphabetical ranking of the halo- gens therefore dictates the direction of numbering. Begin with the carbon that bears bromine ClCHCHBr I-Bromo-1. 2.2-trichloroethane (e) This is a trifluoro derivative of ethanol. The direction of numbering is dictated by the hydroxyl group, which is at C-l in ethanol CF, CHOH 2.2.2-Trifluoroethanol (f) Here the compound is named as a derivative of cyclohexanol, and so numbering begins at the carbon that bears the hydroxyl group cis-3-tert-Butylcyclohexanol (g) This alcohol has its hydroxyl group attached to C-2 of a three-carbon continuous chain; it is named as a derivative of 2-propanol - OH 2-Cyclopentyl-2-propanol (h) The six carbons that form the longest continuous chain have substituents at C-2, C-3, and c-5 when numbering proceeds in the direction that gives the lowest locants to substituents at the first point of difference. The substituents are cited in alphabetical order 5-Bromo-2.3-dimethylhexane Had numbering begun in the opposite direction, the locants would be 2, 4, 5 rather than 2,3,5 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

(b) This compound has the same carbon skeleton as the compound in part (a) but bears a hydroxyl group in place of the bromine and so is named as a derivative of 1-pentanol. (c) This molecule is a derivative of ethane and bears three chlorines and one bromine. The name 2-bromo-1,1,1-trichloroethane gives a lower number at the first point of difference than 1-bromo-2,2,2-trichloroethane. (d) This compound is a constitutional isomer of the preceding one. Regardless of which carbon the numbering begins at, the substitution pattern is 1,1,2,2. Alphabetical ranking of the halo￾gens therefore dictates the direction of numbering. Begin with the carbon that bears bromine. (e) This is a trifluoro derivative of ethanol. The direction of numbering is dictated by the hydroxyl group, which is at C-1 in ethanol. ( f ) Here the compound is named as a derivative of cyclohexanol, and so numbering begins at the carbon that bears the hydroxyl group. (g) This alcohol has its hydroxyl group attached to C-2 of a three-carbon continuous chain; it is named as a derivative of 2-propanol. (h) The six carbons that form the longest continuous chain have substituents at C-2, C-3, and C-5 when numbering proceeds in the direction that gives the lowest locants to substituents at the first point of difference. The substituents are cited in alphabetical order. Had numbering begun in the opposite direction, the locants would be 2,4,5 rather than 2,3,5. 1 2 3 4 5 6 Br 5-Bromo-2,3-dimethylhexane CH3 CH3 OH 2-Cyclopentyl-2-propanol cis-3-tert-Butylcyclohexanol OH 2,2,2-Trifluoroethanol CF3CH2OH 1-Bromo-1,2,2-trichloroethane Cl2CHCHBr Cl Cl3CCH2Br 2-Bromo-1,1,1-trichloroethane CH3 CH3CHCH2CH2CH2OH 4-Methyl-1-pentanol 74 ALCOHOLS AND ALKYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

ALCOHOLS AND ALKYL HALIDES 75 (i) Hydroxyl controls the numbering because the compound is named as an alcohol. 4.23 Primary alcohols are alcohols in which the hydroxyl group is attached to a carbon atom which has one alkyl substituent and two hydrogens. Four primary alcohols have the molecular formula CsHnO. The functional class name for each compound is given in parentheses CH CHCH CHCHOH CH CH, CHCH,OH CH3 I-Pentanol Methyl-l-butanol Pentyl alcohol) CH, CHCH,CHOH CH3CCH,OH 3-Methyl-1-butanol 2. 2-Dimethyl-1-propanol 3-Methylbutyl alcohol) (2, 2-Dimethylpropyl alcohol) Secondary alcohols are alcohols in which the hydroxyl group is attached to a carbon atom which has two alkyl substituents and one hydrogen. There are three secondary alcohols of molecular formula C-H-O CH3CHCH, CH,CH3 CH, CH, CHCH, CH3 CH CHCHCH ethylbutyl alcohol) (-Ethyipropyl alcohol) (1.2-Dimethylpropyl alcohol) Only 2-methyl-2-butanol is a tertiary alcohol(three alkyl substituents on the hydroxyl-bearing OH CH3 CCH, CH3 H3 (1. 1-Dimethylpropyl alcohol) 4.24 The first methylcyclohexanol to be considered is 1-methylcyclohexanol. The preferred chair confor mation will have the larger methyl group in an equatorial orientation, whereas the smaller hydroxyl oup will be axial Most stable conformation of I-methylcyclohexanol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

(i) Hydroxyl controls the numbering because the compound is named as an alcohol. 4.23 Primary alcohols are alcohols in which the hydroxyl group is attached to a carbon atom which has one alkyl substituent and two hydrogens. Four primary alcohols have the molecular formula C5H12O. The functional class name for each compound is given in parentheses. Secondary alcohols are alcohols in which the hydroxyl group is attached to a carbon atom which has two alkyl substituents and one hydrogen. There are three secondary alcohols of molecular formula C5H12O: Only 2-methyl-2-butanol is a tertiary alcohol (three alkyl substituents on the hydroxyl-bearing carbon): 4.24 The first methylcyclohexanol to be considered is 1-methylcyclohexanol. The preferred chair confor￾mation will have the larger methyl group in an equatorial orientation, whereas the smaller hydroxyl group will be axial. OH CH3 Most stable conformation of 1-methylcyclohexanol CH3 OH CH3CCH2CH3 2-Methyl-2-butanol (1,1-Dimethylpropyl alcohol) OH CH3CHCH2CH2CH3 2-Pentanol (1-Methylbutyl alcohol) OH CH3CH2CHCH2CH3 3-Pentanol (1-Ethylpropyl alcohol) CH3 OH CH3CHCHCH3 3-Methyl-2-butanol (1,2-Dimethylpropyl alcohol) CH3 CH3CH2CHCH2OH 2-Methyl-1-butanol (2-Methylbutyl alcohol) CH3 CH3CHCH2CH2OH 3-Methyl-1-butanol (3-Methylbutyl alcohol) CH3 CH3 CH3CCH2OH 2,2-Dimethyl-1-propanol (2,2-Dimethylpropyl alcohol) CH3CH2CH2CH2CH2OH 1-Pentanol (Pentyl alcohol) 4,5-Dimethyl-2-hexanol 6 5 4 3 2 1 OH ALCOHOLS AND ALKYL HALIDES 75 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

76 ALCOHOLS AND ALKYL HALIDES In the other isomers methyl and hydroxyl will be in a 1, 2, 1, 3, or 1, 4 relationship and can be cis or trans in each. We can write the preferred conformation by recognizing that the methyl group will always be equatorial and the hydroxyl either equatorial or axial ans-2-Methylcyclohexanol cis-3-Methylcyclohexanol trans-4-Methylcyclohexanol OH H3C cis-2-Methylcyclohexanol trans-3-Methylcyclohexanol is-4-Methylcyclohexanol 4.25 The assumption is incorrect for the 3-methylcyclohexanols cis-3-Methylcyclohexanol is more stable than trans-3-methylcyclohexanol because the methyl group and the hydroxyl group are both equa- torial in the cis isomer whereas one substituent must be axial in the trans cis-3-Methylcyclohexanol more ans-3-Methylcyclohexanol less stable; smaller heat of combustion stable; larger heat of combustion 4.26(a) The most stable conformation will be the one with all the substituents equatorial CH(CH3)2 The hydroxyl group is trans to the isopropyl group and cis to the methyl group (b All three substituents need not always be equatorial; instead, one or two of them may be axial Since neomenthol is the second most stable stereoisomer. we choose the structure with one axial substituent. Furthermore, we choose the structure with the smallest substituent(the hydroxyl group)as the axial one Neomenthol is shown as follows: H,C H(CH3)2 4.27 In all these reactions the negatively charged atom abstracts a proton from an acid HI HO HO de ion: stronger acid, K (weaker acid, K, =s 10-b) b) CHaCH,O CH COH CHa CHL CH CO Ethoxide Acetic acid: acid Ethanol- Acetate (stronger acid, K,= 10) (weaker aci Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

In the other isomers methyl and hydroxyl will be in a 1,2, 1,3, or 1,4 relationship and can be cis or trans in each. We can write the preferred conformation by recognizing that the methyl group will always be equatorial and the hydroxyl either equatorial or axial. 4.25 The assumption is incorrect for the 3-methylcyclohexanols. cis-3-Methylcyclohexanol is more stable than trans-3-methylcyclohexanol because the methyl group and the hydroxyl group are both equa￾torial in the cis isomer, whereas one substituent must be axial in the trans. 4.26 (a) The most stable conformation will be the one with all the substituents equatorial. The hydroxyl group is trans to the isopropyl group and cis to the methyl group. (b) All three substituents need not always be equatorial; instead, one or two of them may be axial. Since neomenthol is the second most stable stereoisomer, we choose the structure with one axial substituent. Furthermore, we choose the structure with the smallest substituent (the hydroxyl group) as the axial one. Neomenthol is shown as follows: 4.27 In all these reactions the negatively charged atom abstracts a proton from an acid. (a) (b) CH3CH2O CH3COH Ethoxide ion: base Acetic acid: acid (stronger acid, Ka  105 ) CH3CH2OH Ethanol: conjugate acid (weaker acid, Ka  1016) O CH3CO Acetate ion: conjugate base O HI HO H2O Hydrogen iodide: acid (stronger acid, Ka  1010) Hydroxide ion: base I Iodide ion: conjugate base Water: conjugate acid (weaker acid, Ka  1016) OH CH(CH3)2 H3C OH CH(CH3)2 H3C OH CH3 cis-3-Methylcyclohexanol more stable; smaller heat of combustion trans-3-Methylcyclohexanol less stable; larger heat of combustion OH CH3 OH CH3 CH3 H3C cis-2-Methylcyclohexanol trans-3-Methylcyclohexanol cis-4-Methylcyclohexanol OH OH OH CH3 OH CH3 OH H3C trans-2-Methylcyclohexanol cis-3-Methylcyclohexanol trans-4-Methylcyclohexanol 76 ALCOHOLS AND ALKYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website