Chapter 9 Organic Chemistry II

Alkanes

Formulas

CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12

Name

methane ethane propane butane

penta

ne

Formulas

C 6 H 14 C 7 H 16 C 8 H 18 C 9 H 20 C 10 H 22 1. The parent name is that of the

longest continuous

chain of C atoms.

2. An alkane minus one H atom is named as an alk

yl

group.

3. Indicate the locations where replacements are made. Number in the direction that gives the smaller numbers for the locations of the branches.

4. Use prefixes when there is more than one alkyl branches of the same kind & for other types of substituents.

5. Cyclic Alkanes — indicates by

cyclo

before the hydrocarbon name.

Name hexa

ne

hepta

ne

octa

ne

nona

ne

deca

ne

Alkenes

•

Alkenes

, containing at least one carbon-carbon double bond, are

unsaturated hydrocarbons

where n = 1, 2, 3,… (olefin) and have the general formula C n H 2n •

Cis- and Trans- Isomerism

: because of the 

-

bonding, there is not free rotation about the double bond. Therefore, the following isomers are possible: two Cl 's are on the same side of the double bond two Cl 's are on opposite side of the double bond

cis

-dichloroethylene

trans

-dichloroethylene • Nomenclature: 1. Drop

ane

and add

ene

CH 2 =CH 2 eth

ene

CH 2 =CHCH 2 CH 3 (

ethylene

) 1-but

ene

CH 3 CH=CH 2 CH 3 CH=CHCH 3 prop

ene

2-but

ene

Alkenes

2. In naming branched chain alkenes, 1) the

longest continuous chain

must contain the double bond; 2) the double bond is given the

lowest

number.

CH 3 CH 3 CH 2 CH 2 CH 3

4,5-dimethyl-2-hexene

CH 3 CH 2 CH 2 CH 2 CH 3

1,3

-buta

di

ene

1,2

-buta

di

ene 3. Polyenes (have several double bonds): use

prefixes

to denote the number of double bonds and number the longest continuous chain to locate them.

4. Cyclic Olefins: use prefix

cyclo

and number to locate double bonds or radicals on the ring.

cyclo

hexene

1,3

-

cyclo

hexa

di

ene 3-methyl

cyclo

hexene 3,6-dimethyl-

1,4

-

cyclo

hexa

di

ene

Alkynes

•

Alkynes

, containing at least one carbon-carbon triple bond, have the general formula C n H 2n-2 where n = 1, 2, 3,… • Nomenclature: alkynes end in

yne

. Rules of nomenclature are the same as for alkenes. (Note:

alkyl

means any of a series of univalent groups of the general formula C n H 2n+1 derived from

aliphatic hydrocarbons

) CH≡CH eth

yne

(

acetylene

) CH≡CCH 2 CH 3 1-but

yne

CH 3 C≡CH 2 CH 3 C≡CCH 3 prop

yne

2-but

yne

• Cyclic Alkynes and Polyalkynes: 1. The linear nature of the -C≡C- group  small ring alkynes are not stable.

2. Since the −C ≡ C− group is very reactive, poly-ynes are not common.

CH 3 CH 3 CH 2 CH 3 CH 3

5,5-dimethyl-2-hexyne

CH 3 CH 2

2,4-heptadiyne

CH 3

Aromatic Hydrocarbons

• An

aromatic hydrocarbon

is a hydrocarbon of which the molecular structure incorporates one or more planar sets of six carbon atoms that are connected by delocalized electrons. • The term

aromatic

was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent.

CH 2 CH 3 NH 2 NO 2

benzene

nitrobenzene Br

toluene furan

Br 1,3-dibromobenzene

pyridine imidazole

Aryl Groups

phenyl (C 6 H 5 -) benzyl (C 6 H 5 CH 2 -) R-pyridium

Polycyclic Aromatic Hydrocarbons

1-R 1 -3-R 2 -imidazolium

Reactions of Hydrocarbons

•

Alkanes

1. Quite unreactive; used as nonpolar solvents.

2. Reactions involve the substitution of some other element for H.

3. Burned as fuel.

Substitution

light CH 4 (

g

) + Cl 2 (

g

) CH 3 Cl(

g

) + HCl (

g

)

Combustion

CH 4 (

g

) + 2O 2 (

g

) CO 2 (

g

) + 2H 2 O(

l

) D

H

= -890.4 kJ •

Alkenes and Alkynes

1. Addition reactions : add small molecules

across

bond breaks and two s bonds are formed.

the multiple bonds. The  2. If small molecules of HX are added to an unsymmetric alkene or alkyne, the addition is such that the H goes to the C having the greater # of H's.

Addition Addition

CH CH(

g

) + HBr(

g

) CH 2 CH 2 CHBr(

g

) + HBr(

g

) CH 3 CHBr( CHBr 2 (

g g

) )

3. Cracking Pt C 2 H 6 (

g

) catalyst CH 2 CH 2 (

g

) + H 2 (

g

) 4. Hydrogenation CH CH (

g

) + H 2 (

g

) CH 2 CH 2 (

g

) •

Aromatic compounds

1. Aromatic compounds undergo

substitution

rather than

addition

reactions.

2. Benzene and derivatives convert to cyclohexane and derivatives when treated with H 2 at 450 K and 10 atm with a finely divided nickel catalyst. 3. Bz is an excellent ligand in organometallic chemistry of low-valent metals,

e.g.

the sandwich Cr(C 6 H 6 ) 2 and half-sandwich [ RuCl 2 (C 6 H 6 )] 2 complexes

CH 2 CH 3 AlCl 3 + CH 3 CH 2 Cl

Functional Groups

•

Functional group compounds

: Replace a H on a hydrocarbon with a group of atoms other than C and H. Such groups are called

functional groups

. They impart the specific chemical reactivity to the compound.

Organic Halides

•

Organic Halide

:

halogen

replaces a hydrogen on an alkane. • Name halogen

as a radical

: a) Drop the elemental ending on the halogen and add

o

, i.e. -F = fluor

o

, -Cl = chlor

o

, -Br = brom

o

, -I = iod

o

; b) halogen is given the lowest possible number.

CH 3

CH 3 Cl CH 2 Cl 2 chloromethane ( methyl chloride dichloromethane ( ) methylene chloride ) CH Cl 3 C Cl 4 trichloromethane ( chloroform ) tetrachloromethane ( carbon tetrachloride )

CH 3 CH 3

2-iod

o

-3-methylbutane 1,2 dibrom

o

benzene

Organic Halides

• Use: 1.

Starting materials

for other organic compounds because the halogen group is fairly easy to remove.

2.

Solvents

. however the use of halogenated solvents is being phased out because of environmental concerns. Chloroform is a common solvent in the laboratory because it is relatively unreactive, miscible with most organic liquids, and conveniently volatile. It is used as a solvent in the pharmaceutical industry and for producing dyes and pesticides . 3. Coolants ( CCl 2 F 2 = Freon ). The widespread use of chlorofluoro carbons is now thought to be one of the major causes for decrease in the ozone layer.

Carbon tetrachloride is a reagent in synthetic chemistry and was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent. It is a colourless liquid with a "sweet" smell that can be detected at low levels.

Alcohols

•

Alcohol

formula is is formed by replacing a H on an alkane by an

OH

group. General

R-OH

where

R

= hydrocarbon fragment.

1,2-ethane

diol

1, 2, 3 - propane

triol

glycerol or glycerine • Nomenclature : a) the

parent

name is taken from the

l.c.c.

having the OH; b) drop the

e

on the alkane name and add

ol

; c) When necessary, number the

l.c.c.

to locate the OH.

CH 3

4-methyl-2-pentan

ol CH 3 CH 2 CH 3

Classification of Alcohols

• Primary Alcohols : OH is on a C that is bonded to at least two H's. That is, the OH is on an end carbon. Examples: CH 3 OH, CH 3 CH 2 OH • Secondary Alcohols : OH is on a C that is bonded to one H. That is, the C is bonded to two other carbons. Examples: CH 3 CH(OH)CH 3

iso

propanol • Tertiary Alcohols : OH is on a C that is not bonded to a H. That is, the C is bonded to three other carbons..

Examples: CH 3 C(CH 3 )(OH)CH 3 2-methyl-2-propanol (

t

-butyl alcohol)

Production of Ethanol

Biological enzyme C 6 H 12 O 6 (

aq

) 2CH 3 CH 2 OH(

aq

) + 2CO 2 (

g

) Commercial CH 2 =CH 2 (

g

) + H 2 O(

g

) CH 3 CH 2 OH(

g

) Metabolic Oxidation of Ethanol CH 3 CH 2 alcohol OH CH 3 CHO + H 2

Ethers

• An

Ether

is an organic compound that contains an

ether

group – an

O-

atom connected to two alkyl or aryl groups – of general formula R–O–R’. CH 3 OH + HOCH 3 H 2 SO 4 catalyst CH 3 OCH 3 + H 2 O • Nomenclature : the name for simple ethers with no or few other functional groups are a composite of the two substituents followed by ‘

ether

’. For example, CH 3 OC 2 H 5 methyl ethyl ether, C 6 H 5 OC 6 H 5 diphenylether . • CH 3 O = methoxide ion; CH 3 O- = methoxyl group • Used as solvents and anaesthetics • Highly flammable and toxic • Peroxide formation: ethers with a CH group next to the ether O form peroxides. The reaction requires oxygen (or air) and is accelerated by light, metal catalysts and aldehydes. The resulting peroxides can be explosive.

Important Ethers

Ethelene oxide The smallest cyclic ether Dimethyl ether Diethyl ether An aerosol spay propellant A common low boiling solvent (34.6

o C), and an early anaesthetic Dimethoxyethane A high boiling solvent (85 o C) Dioxane Tetrahydrofuran A cyclic ether and high boiling solvent (101 o C) A cyclic ether, one of the most polar simple ethers that is used as a solvent Anisole (methoxybenzene) An aryl ether and a major constituent of the essential oil of anise seed Crown ethers Cyclic polyether that used as phase transfer catalysts.

Polyethylene glycol A linear polyether,

e.g.

used in cosmetics and pharmaceuticals