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Chapter 9. Organic Chemistry II. Alkanes. 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.

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Organic Chemistry II

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Organic chemistry ii

Chapter 9

Organic Chemistry II


Organic chemistry ii

Alkanes

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.


Organic chemistry ii

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

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:

  • Nomenclature:

  • 1. Drop ane and add ene

CH2=CH2 ethene(ethylene)CH3CH=CH2 propene

CH2=CHCH2CH3 1-buteneCH3CH=CHCH3 2-butene


Organic chemistry ii

1,3-butadiene

1,2-butadiene

3,6-dimethyl-1,4-cyclohexadiene

cyclohexene

1,3-cyclohexadiene

3-methylcyclohexene

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.

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.


Organic chemistry ii

2,4-heptadiyne

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-butyneCH3C≡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.

5,5-dimethyl-2-hexyne


Organic chemistry ii

toluene

furan

pyridine

imidazole

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.

benzene


Organic chemistry ii

phenyl (C6H5-)

benzyl (C6H5CH2-)

1-R1-3-R2-imidazolium

R-pyridium

Aryl Groups

Polycyclic Aromatic Hydrocarbons


Organic chemistry ii

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

CH CH(g) + HBr(g) CH2 CHBr(g)

light

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

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

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.

  • Alkenes and Alkynes

  • 1. Addition reactions: add small molecules across the multiple bonds. The  bond breaks and two s 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


Organic chemistry ii

Pt

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

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

catalyst

3. Cracking

4. Hydrogenation

  • Aromatic compounds

  • 1. 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)2and half-sandwich [RuCl2(C6H6)]2 complexes


Organic chemistry ii

2-iodo-3-methylbutane

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


Organic chemistry ii

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.


Organic chemistry ii

1,2-ethanediol

1, 2, 3 - propanetriol

glycerol or glycerine

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.

4-methyl-2-pentanol


Organic chemistry ii

enzyme

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

H2SO4

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

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)CH3isopropanol

  • 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

Metabolic Oxidation of Ethanol

alcohol dehydrogenase

CH3CH2OH CH3CHO + H2


Organic chemistry ii

H2SO4

CH3OH + HOCH3 CH3OCH3 + H2O

catalyst

Ethers

  • An Ether is an organic compound that contains an ethergroup – an -O- atom connected to two alkyl or aryl groups – of general formula R–O–R’.

  • 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.


Organic chemistry ii

Important Ethers


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