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Organic Chemistry Revision
- A hydrocarbon is a compound containing only Hydrogen and Carbon eg, C3H8 propane; C3H6 propene; C3H4 propyne.
- Alkanes - Hydrocarbons with all single bonds (saturated); general formula CnH2n+2; quite unreactive; will react with halogens slowly in the presence of u.v. light ® haloalkanes (substitution reactions); undergo combustion with oxygen. e.g. methane CH4, ethane C2H6, propane C3H8 etc.
- Alkenes - Hydrocarbons with at least one carbon-carbon double bond (unsaturated); general formula (with one double bond) CnH2n; they are quite reactive at the double bond site; react rapidly and vigorously with halogens (addition reactions); undergo combustion with oxygen. e.g. ethene C2H4, propene C3H6 etc.
C3H6 + 9/2 O2 ® 3 CO2 + 3 H2O
C3H8 + 5 O2 ® 3 CO2 + 4 H2O
- Alkanes are separated from ‘crude oil’ by fractional distillation.
- The major use of the alkanes is as fuels.
- Alkenes are produced by catalytic cracking and reformation of alkanes.
- Major uses - high octane additives to petrol
- manufacture of polymers.
- Isomers are substances with the same molecular formulae but different structural formulae.
½ ½ ½ ½ ½ ½ ½ ½ ½
¾ C ¾ C ¾ C ¾ C ¾ C ¾ ¾ C ¾ C ¾ C ¾ C ¾
½ ½ ½ ½ ½ ½ ½ ½ ½
pentane ¾ C ¾ 2-methylbutane
½
¾ C ¾
½ ½ ½
¾ C ¾ C ¾ C ¾ dimethylpropane (or 2,2-dimethylpropane)
½ ½ ½
¾ C ¾
½
Isomers of hexene
½ ½ ½ ½ ½
¾ C Ì C ¾ C ¾ C ¾ C ¾ C ¾
½ ½ ½ ½ ½
hex-1-ene |
CH3 CH2CH2CH3
C Ì C
H H
cis-hex-2-ene |
½ ½ ½ ½ ½
¾ C ¾ C Ì C ¾ C ¾ C ¾ C ¾
½ ½ ½ ½ ½
hex-2-ene |
CH3 H
C Ì C
H CH2CH2CH3
trans-hex-2-ene |
½ ½ ½ ½ ½
¾ C ¾ C ¾ C Ì C ¾ C ¾ C ¾
½ ½ ½ ½ ½
hex-3-ene |
CH3 CH2 CH2CH3
C Ì C
H H
cis-hex-3-ene |
½ ½ ½
¾ C Ì C ¾ C ¾ C ¾ C ¾
½ ½ ½ ½ ½
¾ C ¾
½
2-methylpent-1-ene |
CH3CH2 H
C Ì C
H CH2CH3
trans-hex-3-ene |
also
2-methylpent-2-ene
3-methylpent-1-ene
3-methylpent-2-ene etc.
- Saturated - all single bonds (alkanes)
- Unsaturated - contain at least one carbon-carbon multiple bond (alkenes, alkynes)
- unsaturated hydrocarbons are more reactive; reactive at the multiple bond.
- Polyunsaturated margarines are believed not to result in clogging of the arteries, however saturated fats are believed to cause the deposition of cholesterol into the cell walls of the arteries.
- The alcohols are a homologous series. They have the same general formula (ROH) and the same functional group (ROH). They have similar physical and chemical properties due to the presence of the hydroxyl group (R OH). There is a gradual change in physical properties as the no. of C atoms increases.eg. C22H46, C17H34, C13H24
- Substitution reactions - a H atom is replaced by a halogen; typical reaction of alkanes - very slow reaction in the presence of u.v. light ® haloalkanes
H H
½ u.v. ½
H ¾ C ¾ H + Cl2 ® H ¾ C ¾ H + HCl
½ ½
H Cl
methane chloromethane
- Addition reactions - occur at a double or triple bond; here more bonds are formed. Reaction of alkenes or alkynes with halogens is very rapid. This reaction can be used to distinguish between saturated and unsaturated organic compounds.
H H
H H ½ ½
C Ì C + Br2 ® H ¾ C ¾ C ¾ H
H H ½ ½
Br Br
ethene 1,2-dibromoethane
- Note: Other addition reactions of alkenes include
(i) Reaction with H2 (hydrogenation wtih a catalyst ®alkane
H H
H H catalyst ½ ½
C Ì C + H2 ® H ¾ C ¾ C ¾ H
H H ½ ½
H H
ethene ethane
- Reaction with H2O (hydration) in the presence of an acid catalyst ® alcohol
H H
H H H+ ½ ½
C Ì C + H2O ® H ¾ C ¾ C ¾ H
H H ½ ½
H OH
ethene ethanol
- Addition polymerisation reactions in the presence of a free radical initiator or a catalyst.
- Functional group - an atom or group of atoms that replace one or more hydrogen atoms of an alkane, thus changing the physical and chemical properties. e.g.
Functional group |
Name |
Compounds |
¾ OH |
hydroxyl |
Alcohols or alkanols |
C Ì O |
carbonyl |
Aldehydes or alkanals (if on a terminal C atom)
Ketones or alkanones (if on a mid C atom) |
¾ X |
halogen |
haloalkane |
O
¾ C
OH |
carboxyl group |
alkanoic or carboxylic acid |
¾ NH2 |
amine |
|
O
¾ C
O ¾ |
ester |
esters |
O
¾ C
NH2 |
amide |
amides |
- Fractional distillation is a separation technique used to separate miscible liquids (liquids that dissolve in each other.) The liquids are separated from eachother by heating until the liquid with the lower boiling point begins to boil. this technique is used to separate the alkanes in crude oil. As the no. of C atoms the strength of the dispersion forces also and therefore b.pt.
- Catalytic cracking - is the breaking of larger chain alkanes into smaller hydrocarbons by heating with a catalyst.
e.g. C10H22 ® C8H18 + C2H4
decane catalyst octane ethene
10. (a) H (b) Cl H
½ ½ ½
H ¾ C ¾ Cl Cl ¾ C ¾ C ¾ H
½ ½ ½
Cl Cl H
dichloromethane 1,1,1-trichloroethane
11. (a) CH3 ¾ CH2 ¾ CH ¾ CH3 2-methylbutane
½
CH3
(b) CH3
½
CH3 ¾ CH ¾ CH ¾ CH3 2,3-dimethylpentane
½
CH2
½
CH3
(c) CH2 ¾ CH2 ¾ CH ¾ CH2 ¾ CH3 3-ethylhexane
½ ½
CH3 CH2
½
CH3
(d) CH3
½
CH3 ¾ CH2 ¾ C ¾ CH3 3,3-dimethylhexane
½
CH2
½
CH2
½
CH3
(e) CH3 CH3
½ ½
CH3 ¾ CH2 ¾ CH ¾ CH2 ¾ CH ¾ CH3 2,4-dimethylhexane
(f) CH3 CH3
½ ½
CH3 ¾ C ¾ CH2 ¾ C ¾ CH3 2,2,4,4-tetramethylpentane
½ ½
CH3 CH3
12.
(a) 3,3-dimethylpentane CH3
½
CH3 ¾ CH2 ¾ C ¾ CH2 ¾ CH3
½
CH3
(b) 3-ethylhexane
CH3 ¾ CH2 ¾ CH ¾ CH2 ¾ CH2 ¾ CH3
½
CH2
½
CH3
(c)2,2,4-trimethylpentane
CH3 CH3
½ ½
CH3 ¾ C ¾ CH2 ¾ CH ¾ CH3
½
CH3
(d) 2,3-dimethylhexane
CH3
½
CH3 ¾ CH ¾ CH ¾ CH2 ¾ CH2 ¾ CH3
½
CH3
(e) 3-ethylheptane CH3
½
CH2
½
CH3 ¾ CH2 ¾ CH ¾ CH2 ¾ CH2 ¾ CH2 ¾ CH3
(f) 3-ethyl-2,4-dimethyloctane
CH3
½
CH2
½
CH3 ¾ CH ¾ CH ¾ CH ¾ CH2 ¾ CH2 ¾ CH2 ¾ CH3
½ ½
CH3 CH3
13.
(a) |
2-methylheptanal |
|
(b) |
2,3-dimethylbut-2-ene |
|
(c) |
pent-2-yne |
|
(d) |
cyclohexane |
|
(e) |
2,6-dimethylhept-3-ene |
|
(f) |
oct-3-ene |
|
(g) |
4-ethyl-3-methylhexan-2-one |
|
(h) |
3,4-diethyl-3-methylhexanoic acid |
|
(i) |
3-ethyl-4,5-dipropyloctanal |
|
14.
(a) |
|
2,4-dimethylhept-1-ene |
(b) |
|
pent-1-yne |
(c) |
|
oct-3-ene |
(d) |
|
3,4-dimethylpent-1-ene |
(e) |
|
2,3-dimethylbutane |
(f) |
|
4-ethyl-3-methylheptane |
15. CH3
½
CH3 ¾ C ¾ CH2 ¾ CH ¾ CH2 CH3
½ ½
CH2 CH3
½
CH3
Peter did not use the longest chain to name the compound. (Note mistake in structural formula) It is not 2-ethyl-2,4-dimethylhexane but rather, 3,3,5-trimethylheptane.
16. conc. sulfuric acid
CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
(a) ethanoic acid ethanol ethyl ethanoate water
(b) Esterification (condensation) reaction
(c) (i) Ethanoic acid - changes colour of an indicator e.g. blue litmus to red; reacts with a carbonate releasing carbondioxide gas. (verify with lime water)
(ii) Ethanol - can be oxidised by acidified permanganate to an alkanoic acid which will then react as above. Ethanol also reacts with soium releasing hydrogen gas. (verify with pop test)
(iii) Ethylethanoate - no reaction with carbonate, sodium, permanganate and no effect on blue litmus. Has a strong fruity smell.
(iv) Water - reacts vigorously with sodium; has no effect on blue or red litmus; no effect on permanganate, but boils at 100oC and freezes at O oC
17.
(a) ethyl butanoate |
|
(b) propyl ethanoate |
|
(c) butyl propanoate |
|
18.
(a) |
ethyl ethanoate |
(b) |
propyl ethanoate |
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