KIMIA DASAR

I

SENYAWA ORGANIKMateri tanaman / hewanMakanan, minumanBahan farmasi/ kosmetikPlastik, pipa PVCKomponen minyak bumiPakaian

Unsur kehidupan di atas bumi adalah C

MENGAPA ???

memiliki 4 buah elektron bonding yang

dapat membentuk ikatan kovalen yang kuat,

dapat berupa ikatan tunggal dan rangkap (2

atau 3)

Carbon (C)

H

CH H

H

methane

Carbon has 4 valence electrons

C

H

H

H

H

H C

Ne

Neon

Stable Octet required

Molekul organik paling sederhana:

Covalent Bonding – Atoms Share Electrons

Susunan OKTET yang stabil

metana

ALKANA

C(6) - 1s2, 2s2, 2px1, 2py

1, 2pz0Bentuk dasar

Hibridisasi

C(6) - 1s2, 2s1, 2px1, 2py

1, 2pz1Bentuk

tereksitasi

4 sp3

2s 2px2py 2pz

+ + +

4 X sp3

Struktur tetrahedral pada metana

109.50

Carbon yang menunjukkan hibridisasi sp3 4 buah ikatan C-H yang ekivalen (ikatan )Semua ikatan tunggal dinamakan ikatan

H

CH

HH

Alkana CnH2n+2consist of only carbon and hydrogen bonded by single covalent bonds single

H

CH H

H

H

CH C

H

H

H

H

H

CH C

H

H

C

H

H

H

H

H

CH C

H

H

C

H

H

C

H

H

H

H

CH3

H

CH C

H

H

C

H

H

C

H

H

C

H

H

H

H

methane ethane propane butane

CH3CH3 CH3CH2CH3 CH3CH2CH2CH3

pentane

CH3CH2CH2CH2CH3

Skeletal structure of only carbon atoms

propane

butane

pentane

CH3 CH2 CH2 CH3

CH4

1

4

2 3 4

123

CH3 CH CH2 CH CH2 CH3

CH3CH2 CH3

1 2 3 4 5 6

123456

Contoh :

2-metilbutana

4-etil-2-metilheksana 4 + 2 = 6

3-etil-5-metilheksana 3 + 5 = 8

SIFAT FISIK Senyawa non polar, densitas <1, dengan air

membentuk dua lapisan Larut dalam pelarut organik non polar Alkana C 4, berbentuk gas, Alkana Mr >, berbentuk

cair, Alkana Mr >>>, berbentuk padat Semakin besar jumlah atom C, Mr molekul semakin >,

gaya dispersi tiap molekul >, titik didih semakin tinggi Alkana bercabang td < alkana rantai lurus padanannya Ada pengaruh gaya van der Waals antar molekul Ikatan tunggal mampu berotasi bebas

Melting (blue) and boiling (pink) points of the first 14 n-alkanes in °C.

Isomers – the have the same molecular formula, but a different structuresStructural Isomers – same molecular formula, but atoms are bonded in different orders.

H3C C

CH3

CH3

H

Isobutane

H3C CH

CH3

CH2 CH3

Isopentane

H3C C

CH3

CH3

CH3

Neopentane

Has the same molecular formula as n-pentane, C5H12

Has different Physical Properties : m.p,

b.p.density

C4H10 – has two isomers, n-butane and isobutane (2-methylpropane)

(2,2-dimethylpropane)

(2-methylbutane)

CYCLOALKANES

CnH2n

Bond angles 60°

Bond angles 88°

Bond angles 108°

CyclohexaneBond angles

109.5°

H2C

CH2

CH2C

C

CH

H

H H

H

H Cyclopropane

H2C

H2C CH2

CH2 Cyclobutane

Cyclopentane

H2C

H2C

CH2

CH2

CH2

H2C

CH2

CH2

CH2H2C

H2C

CH3

CH3

CH3

CH3

CH3

C

CH3

1,2-dimetilsikloheksana

tert-butilsiklopentana

metilsikloheksana

How to draw Cyclohexane ?H

HH

H

H

H

put in axial H’s

put in equitorial H’s

H

HH

H

H

H

HH

H

HH

H

H

H

HHH

H

H

H

CH4O2 CO2

H2O energy+ 2 2+ +

RCH2 CH2R RHC CHR H H+alkene

High Temp.catalyst

REACTIONS OF ALKANESCombustion

Dehydrogenation

Halogenation – radical substitution reactions

Br2

Br+ + HBr

light or heat

Halogenation

Substitution Reaction – a reaction in which part of a small reacting molecule replaces an atom or

a group of atoms on the organic molecule

H

CH

H

C

H

H

H + Br2

H

CH

H

C

H

H

Br

Heat or Light or hv

Ethane Bromoethane

HBr+

C

H

H

H + Cl2

Heat or Light or hv

Methane chloromethane

HCl+H C

H

H

ClH

CH2Cl2 and CHCl3may be observed

2104/20/23

Alkyl Halides or Haloalkanes

CH3 CH

Cl

CH CH3

CH3

Cl

CCl Cl

Cl

CH3 CH

Br

CH2 CH2

Cl

F

CH2CH3

BrCl

Cl

CCl F

Cl

F

CCl F

Cl

F

CF

F

C

F

H

H

Naming them

Tetrachloromethaneor carbon tetrachloride

2-Chloro-3-methylbutane 3-Bromo-1-chlorobutane

1-Ethyl-2-fluorocyclohexane1-Bromobutane 2-Chloropropane or

Isopropyl chloride

Tend to be Heavier than waterMore Toxic than Alkanes

Trichlorofluoromethane (Freon-11)

Dichlorodifluoromethane (Freon-12) 1,1,1, 2-Tetrafluoroethane

Chlorofluorocarbons (CFCs)Refrigerant Gases, Ozone Depletion, More H’s more degradable

X

C X = F, Cl, Br

-

Nu -

Electronegativity is defined as the ability of atoms to attract shared electrons in a covalennt bond ------------ leads to nucleophilic substitution in alkyl halides

X is readily displaced by nucleophiles

ClCCl ClCl

Symmetrical molecules have no dipole moment or have equal distribution of electrons within covalent bondsTherefore, they are unreactive!

2404/20/23

STEREOCHEMISTRY

Isomers are different compounds that have the same molecular formula

Structural isomers are isomers that differ because their atoms are connected in a different order

Stereoisomers differ only in the arrangement of their atoms in space

Cl H

Cl H

Cl H

H Cl

cis-1,2-Dichloroethene trans-1,2-Dichloroethene

C2H2Cl2

Geometric Isomers

CH3OCH3 ---- dimethyl ether and CH3CH2OH ---- ethanol

Enantiomers are stereoisomers whose molecules are nonsuperimposable mirror images of one another

Objects that are superimposable on their mirror images are said to be achiral

CH3

CH2

CHHO

CH3

CH2

CH

CH3 CH3OH Interchanging any two groups at a

chiral centre (stereocentre) that

bears four different groups converts

one enantiomer into another

Involves a tetrahedral sp3 atom

CH3 C

OH

CH2 CH3

2-Butanol

H

Chiral Centre

One structure can be superimposed on another

If any of the groups attached to the tetrahedral atom are the same, the centre is achiral.

The ultimate way to test for

molecular chirality is to

construct models of the

molecule and its mirror image

and then determine whether

they are superimposable

A molecule will not be chiral if it possess a centre or plane of Symmetry

2-Propanol

CH3

C OHH

CH3

C

CH3HHO

CH3

Screwdriver is achiralSocks are achiralGolf club is chiralGloves are chiral

What is a chiral object?

What is an achiral object?

Properties of EnantiomersEnantiomers have identical melting points and boiling pointsEnantiomers have identical solubilities in solventsEnantiomers have identical spectra and refractive indexEnantiomers interact, and react with achiral molecules in the same mannerEnantiomers interact and react with other

chiral molecules at different ratesEnantiomers rotate plane-polarised light by equal amounts but in opposite directions

Plane-polarised light

Oscillation of electrical field of ordinary lightoccurs in all possible directions

Polarimeter is a devise used to measure the effect of plane-polarised light on an optically active compound

Chiral molecules are optically active

3104/20/23

No Correlation between the direction of rotation of plane polarised light and the absolute configuration of a molecule

Clockwise Rotation (+) – dextrorotatoryAnti-Clockwise Rotation (-) – levorotatory

C

CH2CH3

H2CCH3

HHO

C

CH2CH3

H2CCH3

HCl

(R)-(+)-2-Methyl-1-butanol (R)-(-)-1-Chloro-2-methylbutanol

Same Configuration

An equimolar mixture of two enantiomers is called a Racemic Mixture It is Optically Inactive

3204/20/23

H

O

S-(+)-Carvone

O

R-(-)-Carvone

H

Principle component of Caraway seed oil and responsible for the characteristic odour

Principle component of Spearmint oil and responsible for the characteristic odour

Receptor Sites in the Nose are Chiral