matriculation chemistry ( hydrocarbon ) part 1 alkane
TRANSCRIPT
Chapter 13.0 HYDROCARBONS
are compounds which
contain only carbon and
hydrogen atoms.
13.1 : ALKANES
Hydrocarbon
ALKANES(saturated)
contain only single bond
ALKENES(unsaturated)
contain C=C
CYCLO-ALKANES (saturated)Alkanes which C atoms are
join in rings
ALKYNES(unsaturated)
containC≡C
CYCLO-ALKENES(unsaturated)
HIDROCARBONS
AROMATIC(contain one or more benzene ring)
ALIPHATIC
• Saturated hydrocarbons
- compound with C-C - Example : alkanes and cycloalkanes
– Contain the maximum number of hydrogen atoms that the carbon compound can possess.
• Unsaturated hydrocarbons
-compounds with multiple bonds -Example : alkenes, cycloalkenes, alkynes and aromatic hydrocarbons
– They posses fewer than the maximum number of hydrogen atoms.
ALKANES
Alkanes are known as saturated hydrocarbon which contain only single covalent bonds.
General formula for straight chain of alkanes is CnH2n+2
where n ≥ 1
General formula for cycloalkanes is CnH2n
where n ≥ 3
Each carbon atom in alkanes is
- sp3 hybridised
- tetrahedral with four sigma bond (formed by the four sp3 hybrid orbitals.)
- all bond angles are close to 109.5o
Alkanes IUPAC names have the –ane suffix.
The First Ten Unbranched Alkanes Molecular formula
Structural formula No .of C atoms
Name
CH4 CH4 1 Methane
C2H6 CH3—CH3 2 Ethane
C3H8 CH3—CH2—CH3 3 Propane
C4H10 CH3—(CH2)2—CH3 4 Butane
C5H12 CH3—(CH2)3—CH3 5 Pentane
C6H14 CH3—(CH2)4—CH3 6 Hexane
C7H16 CH3—(CH2)5—CH3 7 Heptane
C8H18 CH3—(CH2)6—CH3 8 Octane
C9H20 CH3—(CH2)7—CH3 9 Nonane
C10H22 CH3—(CH2)8—CH3 10 Decane
• Starting from C4H10 onwards, the alkanes show the phenomenon of chain isomerism.
• They can exist as linear or branched alkanes.
Example
C4H10
CH3(CH2)2CH3 CH3CH(CH3)2
2-
isobutane
C5H12
IUPAC NOMENCLATURE IUPAC NOMENCLATURE
IUPAC – International Union of Pure and Applied Chemistry
Branched - chain alkanes are named according to the following rules:
Choose the longest continuous chain of carbon atoms; this chain determines the parent name for alkanes.
Examples:
CH3CH2CH2CH2CHCH3
| CH3
Parent name: hexane
CH3CH2CH2CH2CHCH3
CH2
CH3
Parent name : heptane
Number the longest chain beginning Number the longest chain beginning with the with the end of the chain nearer the end of the chain nearer the substituent.substituent.
CH3CH2CH2CH2CHCH3
Example:
CH3 substituent
16 4 235
CH3CH2CH2CH2CH
| CH2
| CH3
substituentCH3
1
2
34567
Use rule number 2 to locate the position of the substituent.
The position and the name of the substituent must be written in front of the parent chain.
CH3CH2CH2CH2CHCH3
Examples:
CH3
2-methylhexane
16 4 235
Substituent
-methyl at C-2
CH3CH2CH2CH2CH CH3
| CH2
| CH3
3-methylheptane
1
2
34567
Substituent
-methyl at C-3
butylbutyl
isopropylisopropyl
propylpropyl
ethylethyl
methylmethyl
substituentname
CH3
CH2CH3
CH2CH2CH3
CHCH3
CH3
CH2CH2CH2CH3
Some Common Substituent GroupsSome Common Substituent Groups
Alkane
methane
propane
butane
ethane
isobutyl
sec-butyl
tert-butyl
neopentyl
CH2CHCH3
CH3
CHCH2CH3
CH3
CH3
CH3
CCH3
CH3
CH2CCH3
CH3
cyclopropyl
cyclobutyl
phenyl
benzyl
C6H5 or
CH2
name substituent
BromoBromo -Br-Br
Chloro Chloro -Cl-Cl
Flouro Flouro -F-F
Iodo Iodo -I-I
HydroxylHydroxyl -OH-OH
AminoAmino -NH-NH22
Cyano Cyano -CN-CN
Nitro Nitro -NO-NO22
If If two or more substituents are presenttwo or more substituents are present, , give each substituent a number give each substituent a number corresponding to its location on the longest corresponding to its location on the longest chain.chain.
the substituent should be listed the substituent should be listed alphabeticallyalphabetically. .
In alphabetizing, the prefixes In alphabetizing, the prefixes di, tri, tetra, di, tri, tetra, sec-, tert- are ignoredsec-, tert- are ignored except except iso and iso and neoneo..
Example: 1 2 3 4 5 6
CH3CHCH2CHCH2CH3
| | CH3 CH2
| CH3
4-ethyl-2-methylhexane
If If two substituentstwo substituents are present on the are present on the same carbon atom, same carbon atom, use that number twice use that number twice
Example: CH3
|3 4 5 6
CH3CH2CCH2CH2CH3
| 2 CH2
| 1 CH3
3-ethyl-3-methylhexane
If If two or more identical substituents two or more identical substituents are are present, use present, use prefixes di-(2 identical prefixes di-(2 identical substituents),tri-(3 identical substituents), substituents),tri-(3 identical substituents), tetra-(4 identical substituents).tetra-(4 identical substituents).
CommaCommas are used to separate numbers s are used to separate numbers from each other.from each other.
Example:Example:
CHCH33CHCH――CH CHCH CH33
| || |
CHCH3 3 CHCH33
2,3-dimethylbutane2,3-dimethylbutane
If there are two chains of equal length as If there are two chains of equal length as the parent chain, choose the the parent chain, choose the chain with chain with the greater number of substituents.the greater number of substituents.
7 6 5 4 3 2 1
2,3,5-trimethyl-4-propylheptane (four substituents)
CH3CH2-CH CH CH CHCH3
| | | | CH3 CH2 CH3 CH3
| CH2
| CH3
4 3 2 1
5
6
7
4-sec-butyl-2,3-dimethylheptane (three substituents)
If branching occurs at an equal distance from If branching occurs at an equal distance from either end of the longest chain, choose the either end of the longest chain, choose the name that gives the name that gives the lower number at the first lower number at the first point of difference.point of difference.
6 5 4 3 2 1
CH3CHCH2CH CHCH3
| | | CH3 CH3 CH3
2,3,5-trimethylhexane
(NOT 2,4,5-trimethylhexane)
1 2 3 4 5 6
CYCLOALKANESCYCLOALKANESCycloalkanes – alkanes which carbon Cycloalkanes – alkanes which carbon atoms are joined in atoms are joined in ringsrings..
Cycloalkanes are known as saturated Cycloalkanes are known as saturated hydrocarbon, because it has the hydrocarbon, because it has the maximum number of bonded hydrogen maximum number of bonded hydrogen ( only has single bonds).( only has single bonds).
General formula: General formula:
CCnnHH2n2n where where n = 3, 4, 5, …… n = 3, 4, 5, ……
NOMENCLATURE OF NOMENCLATURE OF CYCLOALKANESCYCLOALKANES
Cycloalkanes Cycloalkanes with only one ringwith only one ring are are named withnamed with the prefix cyclo- to the the prefix cyclo- to the names of the alkanesnames of the alkanes (contain the (contain the same number of carbon atoms)same number of carbon atoms)
Examples: Monocyclic compounds
C3H6 cyclopropane
C4H8 cyclobutane
C5H10 cyclopentane
If only one substituent is present, it is If only one substituent is present, it is not necessary to designate its positionnot necessary to designate its position..
Examples:Examples:
CH3
Chlorocyclopropane
Methylcyclohexane
Cl
If two substituents are present, If two substituents are present, number carbon in the ring number carbon in the ring beginning with the substituent beginning with the substituent according to the according to the alphabetical orderalphabetical order
and and number in the direction that gives number in the direction that gives the next substituent the next substituent the lowest the lowest numbernumber possible. possible.
Examples:
1-ethyl-2-methylcyclohexaneNOT
1-ethyl-6-methylcyclohexane
CH3
CH2CH31
23
4
5 6
1,3-dichlorocyclopentane(NOT 1,5-
dichlorocyclopentane)
Cl Cl1
2
3
4 5
When three or more substituents are present, begin at the carbon with substituent that leads to the lowest set of locants.
Example:CH2CH3
1-chloro-3-ethyl-4-methylcyclohexane
4- chloro-2-ethyl-1-methylcyclohexane
Cl CH3
Locants
chloro
ethyl
methyl
1
3
4 1
2
4
1
2 3
4
56
1
23
4
5 6
1-ethyl-1,3-dimethylcyclopentane(NOT 3-ethyl-1,3-dimethylcyclopentane)
H3C CH2CH3
CH3
When a single ring system is attached to a single chain with a greater number of carbon atoms
or when more than one ring system is attached to a single chain, then it is appropriate to name the compounds as cycloalkylalkane.
Number of C at ring
Number of C at linear chain
1,3-dicyclohexylpropane
1
2
3
Examples:
CH2CH2CH2CH2CH3
1-cyclobutylpentane