Chapter 4 Alcohols and Alkyl Halides

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Chapter 4Alcohols and Alkyl Halides
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Overview of Chapter
This chapter introduces chemical reactions and
their mechanisms by focusing on two
reactionsthat yield alkyl halides.

• (1) alcohol hydrogen halide
• ROH HX ? RX H2O
• (2) alkane halogen
• RH X2 ? RX HX
• Both are substitution reactions

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4.1Functional Groups
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Functional Group

• a structural unit in a molecule responsible for
  itscharacteristic behavior under a particular
  set ofreaction conditions

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Families of organic compoundsand their
functional groups

• Alcohol ROH
• Alkyl halide RX (X F, Cl, Br, I)
• Amine primary amine RNH2
• secondary amine R2NH
• tertiary amine R3N

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Families of organic compoundsand their
functional groups
Epoxide

• Ether ROR'
• Nitrile RCN
• Nitroalkane RNO2
• Sulfide RSR'
• Thiol RSH

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Many classes of organic compounds contain a
carbonyl group
R
Carbonyl group
Acyl group
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Many classes of organic compounds contain a
carbonyl group
H
R
Carbonyl group
Aldehyde
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Many classes of organic compounds contain a
carbonyl group
R'
R
Carbonyl group
Ketone
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Many classes of organic compounds contain a
carbonyl group
OH
R
Carbonyl group
Carboxylic acid
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Many classes of organic compounds contain a
carbonyl group
OR'
R
Ester
Carbonyl group
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Many classes of organic compounds contain a
carbonyl group
NH2
R
Amide
Carbonyl group
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4.2IUPAC Nomenclatureof Alkyl Halides
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IUPAC Nomenclature
There are several kinds of IUPAC nomenclature.

• The two that are most widely used
  are functional class nomenclature substitutive
  nomenclature
• Both types can be applied to alcohols andalkyl
  halides.

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Functional Class Nomenclature of Alkyl Halides

• Name the alkyl group and the halogen asseparate
  words (alkyl halide)

CH3F
CH3CH2CH2CH2CH2Cl
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Functional Class Nomenclature of Alkyl Halides

• Name the alkyl group and the halogen asseparate
  words (alkyl halide)

CH3F
CH3CH2CH2CH2CH2Cl
Methyl fluoride
Pentyl chloride
1-Ethylbutyl bromide
Cyclohexyl iodide
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Substitutive Nomenclature of Alkyl Halides

• Name as halo-substituted alkanes.
• Number the longest chain containing thehalogen
  in the direction that gives the lowestnumber to
  the substituted carbon.

CH3CH2CH2CH2CH2F
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Substitutive Nomenclature of Alkyl Halides

• Name as halo-substituted alkanes.
• Number the longest chain containing thehalogen
  in the direction that gives the lowestnumber to
  the substituted carbon.

CH3CH2CH2CH2CH2F
1-Fluoropentane
2-Bromopentane
3-Iodopentane
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Substitutive Nomenclature of Alkyl Halides

• Halogen and alkyl groupsare of equal rank when
  it comes to numberingthe chain.
• Number the chain in thedirection that gives the
  lowest number to thegroup (halogen or
  alkyl)that appears first.

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Substitutive Nomenclature of Alkyl Halides
5-Chloro-2-methylheptane
2-Chloro-5-methylheptane
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4.3IUPAC Nomenclatureof Alcohols
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Functional Class Nomenclature of Alcohols

• Name the alkyl group and add "alcohol" as
  aseparate word.

CH3CH2OH
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Functional Class Nomenclature of Alcohols

• Name the alkyl group and add "alcohol" as
  aseparate word.

CH3CH2OH
Ethyl alcohol
1,1-Dimethylbutylalcohol
1-Methylpentyl alcohol
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Substitutive Nomenclature of Alcohols

• Name as "alkanols." Replace -e ending of
  alkanename by -ol.
• Number chain in direction that gives lowest
  numberto the carbon that bears the OH group.

CH3CH2OH
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Substitutive Nomenclature of Alcohols

• Name as "alkanols." Replace -e ending of
  alkanename by -ol.
• Number chain in direction that gives lowest
  numberto the carbon that bears the OH group.

CH3CH2OH
Ethanol
2-Methyl-2-pentanol
2-Hexanol
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Substitutive Nomenclature of Alcohols

• Hydroxyl groups outrank alkyl groups when it
  comes to numberingthe chain.
• Number the chain in thedirection that gives the
  lowest number to thecarbon that bears theOH
  group

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Substitutive Nomenclature of Alcohols
6-Methyl-3-heptanol
5-Methyl-2-heptanol
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4.4Classes of Alcoholsand Alkyl Halides
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Classification

• Alcohols and alkyl halides are classified
  as primary secondary tertiaryaccording to
  their "degree of substitution."
• Degree of substitution is determined by
  countingthe number of carbon atoms directly
  attached tothe carbon that bears the halogen or
  hydroxyl group.

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Classification
H
CH3CH2CH2CH2CH2F
OH
primary alkyl halide
secondary alcohol
secondary alkyl halide
tertiary alcohol
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4.5Bonding in Alcoholsand Alkyl Halides
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Dipole Moments

• alcohols and alkyl halides are polar

?

H
?
?
?
?
H
H
? 1.9 D
? 1.7 D
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Dipole Moments

• alcohols and alkyl halides are polar

? 1.9 D
? 1.7 D
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Dipole-Dipole Attractive Forces
?? ?
?? ?
?? ?
?? ?
? ??
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Dipole-Dipole Attractive Forces
?? ?
?? ?
?? ?
?? ?
? ??
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4.6Physical Properties of Alcohols and Alkyl
HalidesIntermolecular Forces

• Boiling point
• Solubility in water
• Density

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Effect of Structure on Boiling Point
CH3CH2CH3
CH3CH2OH
CH3CH2F
Molecularweight Boilingpoint,
C Dipolemoment, D

• 44 48 46
• -42 -32 78
• 0 1.9 1.7

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Effect of Structure on Boiling Point
CH3CH2CH3
Molecularweight Boilingpoint,
C Dipolemoment, D
Intermolecular forcesare weak. Only
intermolecular forces are induced dipole-induced
dipole attractions.

• 44
• -42
• 0

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Effect of Structure on Boiling Point
CH3CH2F
A polar moleculetherefore dipole-dipoleand
dipole-induceddipole forces contributeto
intermolecular attractions.
Molecularweight Boilingpoint,
C Dipolemoment, D

• 48
• -32
• 1.9

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Effect of Structure on Boiling Point
CH3CH2OH
Highest boiling pointstrongest
intermolecularattractive forces. Hydrogen
bonding isstronger than other dipole-dipole
attractions.
Molecularweight Boilingpoint,
C Dipolemoment, D

• 46
• 78
• 1.7

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Figure 4.4 Hydrogen bonding in ethanol
?
?
?
?
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Figure 4.4 Hydrogen bonding in ethanol
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Boiling point increases with increasingnumber of
halogens
Compound Boiling Point

• CH3Cl -24C
• CH2Cl2 40C
• CHCl3 61C
• CCl4 77C

Even though CCl4 is the only compound in this
list without a dipole moment, it has the highest
boiling point. Induced dipole-induced dipole
forces are greatest in CCl4 because it has the
greatest number of Cl atoms. Cl is more
polarizable than H.
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But trend is not followed when halogenis fluorine
Compound Boiling Point

• CH3CH2F -32C
• CH3CHF2 -25C
• CH3CF3 -47C
• CF3CF3 -78C

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But trend is not followed when halogenis fluorine
Compound Boiling Point

• CH3CH2F -32C
• CH3CHF2 -25C
• CH3CF3 -47C
• CF3CF3 -78C

Fluorine is not very polarizable and induced
dipole-induced dipole forces decrease with
increasing fluorine substitution.
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Solubility in water

• Alkyl halides are insoluble in water.
• Methanol, ethanol, isopropyl alcohol
  arecompletely miscible with water.
• The solubility of an alcohol in waterdecreases
  with increasing number of carbons (compound
  becomesmore hydrocarbon-like).

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Figure 4.5 Hydrogen Bonding Between Ethanol and
Water
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Density

• Alkyl fluorides and alkyl chlorides areless
  dense than water.
• Alkyl bromides and alkyl iodides are more dense
  than water.
• All liquid alcohols have densities of about 0.8
  g/mL.

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4.7Preparation of Alkyl Halides fromAlcohols
and Hydrogen Halides

• ROH HX ? RX H2O

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Reaction of Alcohols with Hydrogen Halides
ROH HX ? RX HOH

• Hydrogen halide reactivity HF HCl HBr HI

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Reaction of Alcohols with Hydrogen Halides
ROH HX ? RX HOH

• Alcohol reactivityCH3OH RCH2OH R2CHOH
  R3COHMethanol Primary Secondary Tertiary

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Preparation of Alkyl Halides
25C
(CH3)3CCl H2O

• (CH3)3COH HCl

78-88
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Preparation of Alkyl Halides
A mixture of sodium bromide and sulfuric acid may
be used in place of HBr.