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Topic 20 - Organic chemistry. Introduction- functional groups and naming Nucleophilic substitution reactions Elimination reactions Condensation reactions Reaction pathways Stereoisomerism. 20.1 Ester. Functional group: -COOC- Condensation reaction or esterification

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topic 20 organic chemistry
Topic 20- Organic chemistry
  • Introduction- functional groups and naming
  • Nucleophilic substitution reactions
  • Elimination reactions
  • Condensation reactions
  • Reaction pathways
  • Stereoisomerism
20 1 ester
20.1 Ester
  • Functional group: -COOC-
  • Condensation 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)

slide3

Esterification

Butanoicacid

Methanol

Name:

  • The alcohol part: Stem + yl: Methyl-
  • The acid part: the salt name; -buthanoate

=> Methyl-buthanoate

slide5

Which names?

Ethylethanoatepropylethanoate

2-butylethanoate penthylpropanoate

amine
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
Amide
  • Functional group: -CONH
  • Name: stem + suffix: -anamide
    • Methanamid H-CONH2
    • EthanamidCH3-CONH2
  • Peptidebond in proteins
nitrile
Nitrile
  • Functional group: -CN
  • Former name: cyanides
  • Name: stem + suffix: nitrile
    • Metanenitrile: HCN
    • Ethanenitrile: CH3-CN
slide9

Nucleophiles and electrophiles- oftenneeded in organicreactions

  • Nucleophile- nucleuslover
  • Has freeelectronpair and whole or part negative charge
  • The larger the negative charge - the better the nucleophile
  • Eg: C=C, H2O, -OH, -CN, NH3
  • Electrophile-electronlover
  • Has wholeor part positive charge
  • The larger the positive charge - the better the Electrophile
  • Eg: C=O, H+, C-Cl,
slide10

20.2 Nucleophilic substitution reactions

Nu: + R-X  Nu-R + X:

It’s important to know the difference of these because they will undergo different forms of nucleophilic substitution reactions

s n 2 or s n 1
SN2 or SN1?

SN2

SN1

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

  • Bimolecular = two species in the rate determining step. Rate = k [org]*[Nu]
  • Primary halogenoalkanes
  • Steric hindrance
  • One-step with transition state
  • Inversion of configuration
factors affecting the rate
Factors affecting the rate
  • The halogen in the halogenoalkaneis 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

s n 2 substitution reaction with ammonia
SN2 substitution reaction with ammonia
  • H3N: + R-X R-NH2 + HX
  • Forming an amine
s n 2 substitution reaction with cn as nucleophile
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
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
20.3 Elimination reactions
  • CH3CH2-Br + OH-CH2=CH2 + H2O + Br-

Condition: 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 + Br-

Will happen in warm dilute solution of sodium hydroxide, the hydroxide ion will work as a nucleophile.

the e1 m echanism similar to s n 1
The E1 mechanism (similar to SN1)
  • Involves heterolytic fission of C-X bond
  • Tertiary halogenalkane
  • Via a carbocation intermediate
the e2 mechanism similar to s n 2
The E2 mechanism (similar to SN2)
  • Concerted bimolecular reaction
  • Primary halogenalkane
  • Via transition state
dehydration reaction of alcohol to form alkene
Dehydration reaction of alcohol to form alkene
  • E1 or E2?
  • Excess of H2SO4, ~170oC
20 4 condensation reaction
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
Esterification

Name: R-yl R’-oate

Esters: flavouring agents (food, perfume), solvents, plastics (polyesters)

H2O

amide condensation
Amide condensation

AmineCarboxylicacidAmideWater

H2O

polycondensations plastics
PolycondensationsPlastics
  • Polyesters: polyethylene terphtalate (PET)
  • Polyamides;nylone
slide24

Benzene-1,4-dicarboxylic acid + Ethane-1,2-diol

Cancondensewith a diol

Cancondensewith a dicarboxylicacid

Monomers withtwofunctionalgroupsarerequired

polyamides
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

hexanedioicacid + 1,6-diaminohexane  Nylon

reaction pathways
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 quarternaryammonum 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

stereoisomerism
Stereoisomerism
  • Different location in space of atoms or groups
slide28

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
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
slide30

cis-but-2-ene-1,4.dioic trans-but-2-ene-1,4.dioic

m.p= 286oC m.p.= 130oC with decomposition.

Strong H-bond between molecules in trans. Strong H-bond in the molecule in cis.

optical
Optical

mirror plane

enantiomers to each other

slide33

Stereo isomers Different location in space.

Geometric

cis-2-buten trans-2-buten

Optical

mirror plane

enantiomers to each other

slide34

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
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