Topic 20 - Organic chemistry
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Introduction- functional groups and naming
Nucleophilic substitution reactions
Elimination reactions
Condensation reactions
Reaction pathways
Stereoisomerism
20.1 Ester
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Functional group: -COOCCondensation reaction or esterification
Many fruit-smelling esters
The bond in triglycerides (lipids)
• Alcohol + carboxylic acid  ester + water
• CH3-OH + HOOC-CH3  CH3OOC-CH3 + H2O
(The underlined forms water)
Esterification
Butanoic acid
Methanol
Name:
– The alcohol part: Stem + yl: Methyl– The acid part: the salt name; -buthanoate
=> Methyl-buthanoate
Which names?
Which names?
Ethylethanoate
2-butylethanoate
propylethanoate
penthylpropanoate
Amine
• Relatives to ammonia => weak bases
• Functional group –NH2
• H-bonds => higher bp’s, smaller ones are
water-soluble etc.
• Name: stem + suffix: -ylamine (or prefix amino-)
– Methylamine CH3-NH2
– Ethylamine CH3-CH2-NH2
Amide
• Functional group: -CONH
• Name: stem + suffix: -anamide
– Methanamid H-CONH2
– Ethanamid CH3-CONH2
• Peptide bond in proteins
Nitrile
• Functional group: -CN
• Former name: cyanides
• Name: stem + suffix: nitrile
– Metanenitrile: HCN
– Ethanenitrile: CH3-CN
Nucleophiles and electrophiles- often
needed in organic reactions
• Nucleophile- nucleus
lover
• Has free electronpair
and whole or part
negative charge
• The larger the negative
charge - the better the
nucleophile
• Eg: C=C, H2O, -OH, -CN,
NH3
• Electrophile-electron
lover
• Has whole or part
positive charge
• The larger the positive
charge - the better the
Electrophile
• Eg: C=O, H+, C-Cl,
H
H
H
H
C
20.2 Nucleophilic substitution
reactions
H
C
P r im a r y C w it h C l a n d 2 H
Cl
Nu: + R-X  Nu-R + X:
H
H
H
Cl
H
C
C
C
H
H
H
H
Cl
H
C
C
C
H
C H3
H
H
S e c o n d a r y C w it h C l a n d 1 H
H
T e r t ia r y C w it h C l a n d 0 H
It’s important to know the difference of these because they
will undergo different forms of nucleophilic substitution
reactions
SN2 or SN1?
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S N2
Bimolecular = two species in
the rate determining step.
Rate = k [org]*[Nu]
Primary halogenoalkanes
Steric hindrance
One-step with transition
state
Inversion of configuration
S N1
• Monomolecular = one species
in the rate determining step.
Rate = k [org]
• Tertiary halogenalkanes
• Heterolytic fission of substrate
rate determining step
• Formation of inermediate
carbocation
• Racemix mixture formed
Factors affecting the rate
• The halogen in the halogenoalkane is
important for the reaction rate:
C-I > C-Br > C-Cl > C-F (cf. bond strength)
• The stronger the nucleophile, the faster the
SN2-reaction
CN- > OH- > NH3 > H2O
SN2 substitution reaction with
ammonia
H3N: + R-X  R-NH2 + HX
Forming an amine
SN2 substitution reaction with CN- as
nucleophile
R-X + CN- 
R-CN + X- Forming a nitrile
The carbon chain will be prolonged with one carbon atom
Reactions with nitriles
• Nitrile + H2  Ni catalyst  Amine
CH3CH2-CN + H2/Ni  CH3CH2-NH2
• Nitrile + Acidic water  Carboxylic acid
CH3CH2-CN + H+/H2O  CH3CH2-COOH
20.3 Elimination reactions
• CH3CH2-Br + OH-  CH2=CH2 + H2O + BrCondition: Hot and concentrated sodium hydroxide
solution in ethanol. Reflux.
• Opposite to addition reaction
• 2 kinds; E1 and E2
• If the conditions are different: A substitution reaction
CH3CH2-Br + OH-  CH3CH2-OH + BrWill happen in warm dilute solution of sodium hydroxide, the
hydroxide ion will work as a nucleophile.
The E1 mechanism (similar to SN1)
• Involves heterolytic fission of C-X bond
• Tertiary halogenalkane
• Via a carbocation intermediate
The E2 mechanism (similar to SN2)
• Concerted bimolecular reaction
• Primary halogenalkane
• Via transition state
Dehydration reaction of alcohol to form alkene
• E1 or E2?
• Excess of H2SO4, ~170oC
20.4 Condensation reaction
• 2 Organic molecules  1 Organic molecule + water
• Acid catalysed
• Esterification, etherification
• Common in biochemistry, formation of polysaccharides,
proteins, nucleic acids
Esterification
H
O
H
H
H
H
C
C
H
H
O
H
C
C
H+
H
C
C
H
H
E th a n o l
OH
HO
C
C
H
E t a n o ic a c id
H
H
O
E t y le t h a n o a t e
Name: R-yl R’-oate
Esters: flavouring agents (food, perfume),
solvents, plastics (polyesters)
H
H
+
H2O
W a te r
Amide condensation
H
H
H
C
C
H
H
HO
N H2
O
H
C
C
H
H
H
Amine
Carboxylic acid
H
H
C
C
H
H
C H3
A la n in e
COH
HN
C
C
H
+
H
H 2O
H
Water
O
O
CH
H
Amide
H
H2N
N
O
CH
H
G ly c in e
COOH
H2N
CH
C H3
C
N
C H2
H
D ip e p t id e o f a la n in e a n d g ly c in e
COOH
+
H2O
Polycondensations
Plastics
• Polyesters: polyethylene terphtalate (PET)
• Polyamides; nylone
Benzene-1,4-dicarboxylic acid + Ethane-1,2-diol
Can condense with a diol
Can condense with a dicarboxylic acid
Monomers with two functional groups are required
Polyamides
HOOC-R-COOH + H2N-R’-NH2  H2N-R’-NH-OC-R-COOH
Di-amine
amide bond
HOOC-(CH2)4-COOH + H2N-(CH2)6-NH2 
 HOOC-(CH2)4-CONH-(CH2)6-NH2 + water
hexanedioic acid + 1,6-diaminohexane  Nylon
20.6 Reaction pathways
1. Elimination reaction. Hot, concentrated and reflux
2. Substitution reaction. SN1 or SN2
3. Substitution reaction. SN1 or SN2. (Can be substituted up 4 times to a
quarternary ammonum salt)
4. Condensation reaction. Acid catalyst (or alkaline catalyst, but more common
when hydrolysis of ester). Equilibrium reaction.
5. Condensation reaction. Acid catalyst (or alkaline catalyst). Equilibrium
reaction.
6. Nitrile to amin: Reduction with H2 and Ni-catalyst
20.5 Stereoisomerism
• Different location in space of atoms or groups
Structural isomers
• Chain:
e.g. n-butane : methylpropane
• Positional:
e.g. 1-propanol : 2-propanol
• Functional groups:
Ethanoic acid, CH3-COOH : Methyl methanoate HCOOCH3
Propanal, CH3-CH2-CHO : Propanone, CH3-CO-CH3
Geometric
• Double bond = p and s bonds. No free rotation around a
double
cis-2-buten
trans-2-buten
• cis-1,2-dichloroethane: bp = 60.3oC
• trans-1,2-dichloroethane: b.p. = 47.5oC
cis-but-2-ene-1,4.dioic
1,4.dioic
trans-but-2-ene-
m.p = 286oC
m.p.= 130oC with decomposition.
• Strong H-bond between molecules in trans. Strong H-bond in the
molecule in cis.
Cyclic compounds
can also give geometric isomers
• Cis and trans
Optical
mirror plane
enantiomers to each other
Stereo isomers
Different location in space.
Geometric
cis-2-buten
trans-2-buten
Optical
mirror plane
enantiomers to each other
• A carbon with 4 different substituents is said to have an
asymmetric centre or to be chiral.
• Chiral can also mean the whole molecule.
• Enantiomers have the same physical properties except that
they rotate the plane of polarised light in different directions.
• Very important which form of the enantiomer in biology and
medicine.
Polarimeter
• Light: Electromagnetic radiation. Normal light
oscillating in all directions.
• Plane-polarized light: When normal light is sends
throuhg a polarizing filter only waves in the same plan
can pass. If two polarizing filters places 90o to each
other the light will be compleataly blocked.
• Polarimeter: Measure how much the light will rotate
when pass through a solution with optically avtive
substance. A sample holder between two filter