Organic Chemistry IIOrganic Chemistry II

Chapter 9Chapter 9

Alkanes

Formulas Name Formulas NameCH4 methane C6H14 hexane

C2H6 ethane C7H16 heptane

C3H8 propane C8H18 octane

C4H10 butane C9H20 nonane

C5H12 pentane C10H22 decane

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 alkyl 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.

Alkenes• Alkenes, containing at least one carbon-carbon double bond, are unsaturated hydrocarbons (olefin) and have the general formula CnH2n where n = 1, 2, 3,…

• Cis- and Trans- Isomerism: because of the -bonding, there is not free rotation about the double bond. Therefore, the following isomers are possible:

CH2=CH2 ethene (ethylene) CH3CH=CH2 propene

CH2=CHCH2CH3 1-butene CH3CH=CHCH3 2-butene

cis-dichloroethylene trans-dichloroethylene

C C

Cl Cl

H H

C CC CC C

Cl Cl

H H

C C

Cl H

H Cl

C CC CC C

Cl H

H Cl

two Cl 's are on the same side of the double bond

two Cl 's are on opposite side of the double bond

• Nomenclature:

1. Drop ane and add ene

Alkenes2. In naming branched chain alkenes, 1) the longest continuous chain must contain the double bond; 2) the double bond is given the lowest number.

1 2 3 4

5

6CH3 CH CH2 CH CH2 CH3

CH3

CH3

1 2 3 4

5

6CH3 CH CH2 CH CH2 CH3

CH3

CH3

4,5-dimethyl-2-hexene

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.

CH2 CH CH CH21 2 3 4CH2 CH CH CH21 2 3 4 1,3-butadiene

1,2-butadieneCH2 C CH CH31 2 3 4CH2 C CH CH31 2 3 4

cyclohexene 1,3-cyclohexadiene 3-methylcyclohexene3,6-dimethyl-1,4-cyclohexadiene

Alkynes• Alkynes, containing at least one carbon-carbon triple bond, have the general formula CnH2n-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 CnH2n+1 derived from aliphatic hydrocarbons)

CH≡CH ethyne (acetylene) CH3C≡CH2 propyne

CH≡CCH2CH3 1-butyne CH3C≡CCH3 2-butyne

• 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.

1 2 3 4 5 6CH3 C C CH2 C CH3

CH3

CH3

1 2 3 4 5 6CH3 C C CH2 C CH3

CH3

CH3

5,5-dimethyl-2-hexyne

1 2 3 4 5 6 7CH3 C C C C CH2 CH31 2 3 4 5 6 7CH3 C C C C CH2 CH3

2,4-heptadiyne

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.

furan

pyridine imidazole

Cl

chlorobenzene

NH2

aminobenzene

NO2

nitrobenzene

12

3

4

5

6

CH2CH3

ethylbenzene

Br

Br

1,2-dibromobenzene

Br

Br1,3-dibromobenzene

ClCl

chlorobenzene

NH2NH2

aminobenzene

NO2

nitrobenzene

NO2NO2

nitrobenzene

12

3

4

5

61

2

3

4

5

6

CH2CH3CH2CH3

ethylbenzene

Br

Br

Br

Br

1,2-dibromobenzene

Br

Br

Br

Br1,3-dibromobenzene

benzene

toluene

Aryl Groups

Polycyclic Aromatic Hydrocarbons

phenyl (C6H5-)

benzyl (C6H5CH2-) R-pyridium 1-R1-3-R2-imidazolium

Reactions of Hydrocarbons• Alkanes1. Quite unreactive; used as nonpolar solvents.

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

3. Burned as fuel.

Combustion CH4(g) + 2O2(g) CO2(g) + 2H2O(l) H = -890.4 kJ

Substitution CH4(g) + Cl2(g) CH3Cl(g) + HCl (g)light

• Alkenes and Alkynes1. Addition reactions: add small molecules across the multiple bonds. The bond breaks and two bonds are formed.

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) CH2 CHBr(g)

CH2 CHBr(g) + HBr(g) CH3CHBr2(g)

3. Cracking

C2H6(g) CH2 CH2(g) + H2(g)Pt

catalyst

4. Hydrogenation

CH CH(g) + H2(g) CH2 CH2(g)

• Aromatic compounds1. Aromatic compounds undergo substitution rather than addition reactions.

2. Benzene and derivatives convert to cyclohexane and derivatives when treated with H2 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(C6H6)2 and half-sandwich [RuCl2(C6H6)]2 complexes H

H

H

H

H

H

CH2CH3

H

H

H

H

H

+ HCl+ CH3CH2ClAlCl3

catalyst

H

H

H

H

H

H

H

H

H

H

H

H

CH2CH3

H

H

H

H

H

CH2CH3

H

H

H

H

H

+ HCl+ CH3CH2ClAlCl3

catalyst

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 = fluoro, -Cl = chloro, -Br = bromo, -I = iodo; b) halogen is given the lowest possible number.

CH3Cl chloromethane (methyl chloride)

CH2Cl2 dichloromethane (methylene chloride)

CHCl3 trichloromethane (chloroform)

CCl4 tetrachloromethane (carbon tetrachloride)1,2-

dibromobenzene

Br

Br

Br

Br

2-iodo-3-methylbutane

CH3 CH CH CH3

I

1 2 3 4

CH3

CH3 CH CH CH3

I

1 2 3 4

CH3

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 (CCl2F2 = 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 is formed by replacing a H on an alkane by an OH group. General formula is R-OH where R = hydrocarbon fragment.

• 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.

CH3 CH CH2 CH

OH CH3

CH3CH3 CH CH2 CH

OH CH3

CH34-methyl-2-pentanol

1,2-ethanediol 1, 2, 3 - propanetriolglycerol or glycerine

CH3CH2OH CH3CHO + H2

alcohol dehydrogenase

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: CH3OH, CH3CH2OH

• Secondary Alcohols: OH is on a C that is bonded to one H. That is, the C is bonded to two other carbons. Examples: CH3CH(OH)CH3 isopropanol

• 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: CH3C(CH3)(OH)CH3 2-methyl-2-propanol (t-butyl alcohol)

Production of Ethanol

Biological C6H12O6(aq) 2CH3CH2OH(aq) + 2CO2(g)enzyme

Commercial CH2=CH2(g) + H2O(g) CH3CH2OH(g)H2SO4

Metabolic Oxidation of Ethanol

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’.

CH3OH + HOCH3 CH3OCH3 + H2OH2SO4

catalyst

• 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, CH3OC2H5 methyl ethyl ether, C6H5OC6H5 diphenylether.

• CH3O- = methoxide ion; CH3O- = 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 An aerosol spay propellant

Diethyl etherA common low boiling solvent (34.6oC), and an early anaesthetic

Dimethoxyethane A high boiling solvent (85oC)

DioxaneA cyclic ether and high boiling solvent (101oC)

TetrahydrofuranA 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 ethersCyclic polyether that used as phase transfer catalysts.

Polyethylene glycol

A linear polyether, e.g. used in cosmetics and pharmaceuticals