chapter 04 alcohols and alkyl halides - · pdf filechapter 04 alcohols and alkyl halides part...

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2012 Gregory R Cook

Chapter 04Alcohols and Alkyl Halides

part 01

CHEM 341: Spring 2012

Prof. Greg Cook

cook.chem.ndsu.nodak.edu/chem341

Wednesday, February 8, 12

http://cook.chem.ndsu.nodak.edu/chem341http://cook.chem.ndsu.nodak.edu/chem341

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Functional Groups

A functional group is a structural feature in a molecule that has characteristic reactivity.

A functional group has similar behavior in every molecule that contains it.

2

Carbon-Carbon Multiple Bonds

Alkenes - double bonds

CH2 CH2

Alkynes - triple bonds

C C

Arenes - aromatic rings

Carbon-Other atom Single Bonds

OH

Alcohols

Br

Hallides

NH2

Amines

OCH3

Ethers

SH

Thiols

SCH3

Sulfides

Carbon-Oxygen Double Bonds (Carbonyls)

H

AldehydeO

KetoneO

OH

AcidO

OCH3

EsterO

NH2

AmideO

Cl

Acid HalideO

H H

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2012 Gregory R Cook

Functional Groups

A functional group is a structural feature in a molecule that has characteristic reactivity.

A functional group has similar behavior in every molecule that contains it.

2

Carbon-Carbon Multiple Bonds

Alkenes - double bonds

CH2 CH2

Alkynes - triple bonds

C C

Arenes - aromatic rings

Carbon-Other atom Single Bonds

OH

Alcohols

Br

Hallides

NH2

Amines

OCH3

Ethers

SH

Thiols

SCH3

Sulfides

Carbon-Oxygen Double Bonds (Carbonyls)

H

AldehydeO

KetoneO

OH

AcidO

OCH3

EsterO

NH2

AmideO

Cl

Acid HalideO

H HR OH R Xalcohols alkyl halides

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Reactions of Functional Groups

3

H XR OH + H OHR X +

OHR X + R OH + X

X XR H + H XR X +

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General Reaction Classes

Addition Reactions - two or more molecules combine to form a new product

Elimination Reactions - a molecule breaks apart into two or more molecules

Substitution Reactions - part of a molecule is substituted for another group

Rearrangement Reactions - A molecule does not gain or lose atoms, but reorganizes its bonds or groups. Also called isomerization.

4

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General Reaction Classes

Addition Reactions

Elimination Reactions

Substitution Reactions

Rearrangement Reactions

5

A + B C C CH

H

H

H+ H2 cat. C C

H

HHH

H

H

CA B + BA C + H3C Cl + OH H3C OH + Cl

BA heatO O

A + BC cat.OH

H

+ HOH

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Organic halogen compounds are found in many places from common solvents for chemistry and industry, to refrigerants (largely banned for their ozone destruction properties) and natural products.

Alkyl Halides

6

CH2Cl2CHCl3CH2Cl-CH2Cl

commonsolvents

CFCs(chlorofluorocarbons)

CF2Cl2

natural products(epibatidine)

NH

N

Cl

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Alkyl halides are often named using common naming (functional class) considering the alkyl group as a substituent on the halide.

Alkyl Halide Nomenclature

7

methyl bromide

H3C BrI

cyclopentyl iodide 1-methylpropyl chloride

Cl

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IUPAC naming is best using the carbon chain as the parent and the halogen as a halo- substituent

Alkyl Halide Nomenclature

8

bromomethane

H3C BrI

iodocyclopentane 2-chlorobutane

Cl

Br Br

4-bromo-2-methylhexane 2-bromo-4-methylhexane

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Alcohols are often named using common naming (functional class) considering the alkyl group as a substituent on the OH functional group.

Alcohols

9

methyl alcohol

H3C OHOH

cyclopentyl alcohol isopropyl alcohol

OH

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IUPAC naming is best using the carbon chain as the parent and replacing the -ane ending with -anol

note: alcohols outrank alkyl substituents

Alcohol Nomenclature

10

methanol

H3C OHOH

cyclopentanol 2-propanol

OH

OH OH

5-methyl-3-hexanol 4-methyl-2-hexanol

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Alcohols and alkyl halides are classified according to the degree of alkyl substituion on the carbon the functional group is attached

Classes of Alkyl Halides and Alcohols

11

OH

1-propanola primary alcohol

2-chloro-2-methylbutanea tertiary halide (chloride)

Cl OH

trans-3-methylcyclopentanola secondary alcohol

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Reactivity is dominated by the polarity of the C-X bond

Properties of Alkyl Halides

12

fluoromethane CH3-F 1.85 1.39 108

chloromethane CH3-Cl 1.87 1.78 84

bromomethane CH3-Br 1.81 1.93 70

iodomethane CH3-I 1.62 2.14 56

diopole moment(Debyes)

bond length()

bond strength(kcal/mol)

= 1.9 D

C Cl

H

H

H

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Acohols are polar but have other reactive features

Properties of Alcohol

13

weakly acidic

RO

H

weakly basic

= 1.7 D

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Boiling Points of Halides and Alcohol

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Intermolecular Forces

15

Induced dipole/induced dipole (London forces, van der Waals attraction)

Dipole/induced dipole forces Diplole/Dipole forces

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Intermolecular Forces

16

bp -24 C

RO

H

= 1.7 D = 1.9 D

C Cl

H

H

H

bp 65 C

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At about 5 kcal/mol, H-bonds are weaker than covalent bonds but stronger than many other intermolecular forces

Hydrogen Bonding

17

RO

H

+

R

O H +

hydrogenbond

R

OH+

hydrogenbond

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Polarizability - the ability to distort (polarize) electrons in a bond

Polarizability

18

chloromethanebp -24 C

C Cl

HH

H

C Cl

ClH

H

C Cl

ClCl

H

C Cl

ClCl

Cl

dichloromethanebp 40 C

trichloromethanebp 61 C

tetrachloromethanebp 77 C

fluroethanebp -32 C

C F

HH

C

1,1-difluoroethanebp -25 C

1,1,1-trifluoroethanebp -47 C

hexafluoroethanebp -77 C

HH

H

C F

FH

CH

H

H

C F

FF

CH

H

H

C F

FF

CF

F

F

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Alcohols are similar to water but the solubility decreases as the hydrocarbon chain increases

Alcohol Solubility

19

CH3 OH

AlcoholSolubility in Water(g/100 g H2O)

CH3CH2 OH

OH

OH

OH

OH

OH

OH

OH

miscible

miscible

miscible

9

2.7

0.6

0.18

0.054

insoluble

Carbons

1

2

3

4

5

6

7

8

10

Wednesda