4. Types of Hydrocarbons
1- Alkanes with a general formula (CnH2n+2)
2- Alkenes with a general formula (CnH2n)
3- Alkynes with a general formula (CnHn)
5. Timberlake LecturePLUS 5
Alkanes (Paraffin)
Contain C and H only
Contain single bonds C-C
Have 4 bonds to every carbon (C) atom
Are nonpolar
6. Physical properties
Non-polar or only weakly polar, cannot form hydrogen bond
relatively weak intermolecular forces
Lower mp/bp; increase with size; decrease with branching
@ room temperature:
C1 – C4 are gases
C5 – C17 are liquids
> C17 are solids
alkanes are water insoluble
7. Nomenclature of alkanes and cycloalkanes
Trivial names or common names
IUPAC system (international Union of Pure and Applied Chemistry)
In this system we use a suffix and a prefix
Suffix for all alkanes (ane)
Prefix according to number of carbon atoms as following
10. Timberlake LecturePLUS 10
Learning Check Alk1
A. What is the condensed formula for
H H H H
H C C C C H
H H H H
B. What is its molecular formula?
C. What is its name?
14. - Locate the longest continuous chain of carbon atoms; this chain determines the
parent name for the alkane, this chain may or may not be shown in a straight line
CH3CH2CH2CH2CHCH3
CH3
CH3CH2CH2CH2CH
CH2
CH3
CH3
Longest chain (parent) is hexane Longest chain (parent) is heptane
- Number the longest chain (parent), beginning with the end of the chain nearer the
substituent
CH3CH2CH2CH2CH
CH2
CH3
CH3
CH3CH2CH2CH2CHCH3
CH3
1
2
3
4
5
6
Substituent 1
2
3
4
5
6
7 Substituent
17. - When two chains of equal length compete for selection as the parent chain,
choose the chain with the greater number of substituents.
CH3CH2 CH
CH3
CH
CH2
CH2
CH3
CH CH
CH3 CH3
CH3
1
2
3
4
5
6
7
2,3,5-Trimethyl-4-propylheptane (four substituents)
- When branching first occurs at an equal distance from either end of the
longest chain, choose the name that gives the lower number at the first point of
difference
1
2
3
4
5
6
CH3 CH CH2 CH
CH3 CH3
CH
CH3
CH3
2,3,5-Trimethylhexane
(not 2,4,5-trimethylhexane)
18. “Classes of Carbons”
primary carbon (1o) – a carbon bonded to one carbon
secondary carbon (2o) – a carbon bonded to two carbons
tertiary carbon (3o) – a carbon bonded to three carbons
quaternary carbon (4o) – a carbon bonded to four carbons
CH3 CH3
CH3CHCH2CH2C-CH3
CH3
19. Classification of Hydrogen atoms
H2C CH
CH3
CH3
H3C
2o
hydrogen atom 1o
hydrogen atom
3o
hydrogen atom
1o
hydrogen atom
2-Methylbutane
20. Synthesis of alkanes and cycloalkanes
1- Hydrogenation of alkenes:
propene propane
cyclohexene cyclohexane
Ni / ethanol
25o / 50 atm
Ni / ethanol
25o
/ 50 atm
Alkenes react with hydrogen in the presence of metal catalyst such
as nickel and platinum to produce alkanes
21. 2- Reduction of alkyl halide
Br
isopentyl bromide
isopentane
(1-bromo-3-methylbutane)
(2-methylbutane)
H
Zn
A- Most alkyl halides react with zinc and aqueous acid to produce
an alkane. In theses reactions zinc atoms transfer electrons to the
carbon atom of the alkyl halide. Therefore, the reaction is a
reduction of the alkyl halide.
22. A- with an active metal and an acid
R—X + metal/acid RH
active metals = Sn, Zn, Fe, etc.
acid = HCl, etc. (H+)
CH3CH2CHCH3 + Sn/HCl CH3CH2CH2CH3 + SnCl2
Cl
sec-butyl chloride n-butane
CH3 CH3
CH3CCH3 + Zn/H+ CH3CHCH3 + ZnBr2
Br
tert-butyl bromide isobutane
23. B. Reduction of an alkyl halide
b) hydrolysis of a Grignard reagent (two steps)
i) R—X + Mg RMgX (Grignard reagent)
ii) RMgX + H2O RH + Mg(OH)X
CH3CH2CH2-Br + Mg CH3CH2CH2-MgBr
n-propyl bromide n-propyl magnesium bromide
CH3CH2CH2-MgBr + H2O CH3CH2CH3 + Mg(OH)Br
propane
24. Reactions of alkanes:
alkane + H2SO4 no reaction (NR)
alkane + NaOH NR
alkane + Na NR
alkane + KMnO4 NR
alkane + H2,Ni NR
alkane + Br2 NR
alkane + H2O NR
(Alkanes are typically non-reactive. They don’t react with
acids, bases, active metals, oxidizing agents, reducing agents,
halogens, etc.)
25. The main reason for unreactivity of alkanes are:
1- The C-C and the C-H bonds are strong bonds.
2- Neither H nor C atoms in the paraffins have any unshared
electrons or any orbitals in their valency shells not
completely filled
3- No dipole moment between any C-C or C-H
26. Reactions of alkanes
Alkanes and cycloalkanes are relatively unreactive compared with
organic compounds containing functional groups
1) Halogenation
CH4 CH3Cl
UV
+
light other product
-The reaction of an alkane with a halogen is a substitution
reaction
-The halogenation of alkanes take place by a radical mechanism
- High temperature is needed
Photochemical or thermal halogenation
R H + X2 R X + HX
28. Chain propagation remain until either
1- All the Cl2 or CH4 is consumed, or
2- the process is terminated by the following reactions:
A- the recombination of Cl. Atoms to form Cl2 molecules
B- the recombination of the CH3
. to form CH3-CH3
29. Bromine is less reactive toward alkanes than chlorine, but
bromine is more selective in the site of attack
Br2
Br
Br
light / 127o +
(>99%)
(trace)
Cl2
Cl
Cl
light / 25o +
(37%)
(63%)
- Direct iodination is rarely carried out
- Flourine is much more reactive than chlorine, is even less selective than
chlorine
![Medicinal chemistry I
PHC 211
Credit Hour =3
[2 Theoretical +1 Practical
(2 Contact hours)]
الدوائية الكيمياء
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1](https://image.slidesharecdn.com/random-220727155745-b6badd3b/85/organic-cemstry-1-320.jpg)
