INTRO TO ORGANIC CHEMISTRY.pdf

INTRODUCTION TO ORGANIC CHEMISTRY

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TOPICS 1.1 Introduction to Organic Chemistry 1.2 Alkanes and Cycloalkanes 1.3 Alkenes and Alkynes 1.4 Aromatic Compounds 1.5 Alkyl Halides 1.6 Alcohols 1.7 Aldehydes and Ketones 1.8 Carboxylic Acids and their Derivatives 1.9 Amines

INTRODUCTION TO ORGANIC CHEMISTRY

Structural Formulas of Organic Molecules Ways of Depicting the Organic Molecules Classification of Carbon and Hydrogen

Atoms in Organic Molecules Functional Groups and Homologous

Series Isomerism in Organic Molecules Introduction to Organic Molecules

Reactions

Organic chemistry is a branch of chemistry that focuses on compounds that contain carbon except CO, CO2, carbonates, and carbides

Even though organic compounds only contain a few elements, the unique ways carbon atoms can attach together to form molecules leads to millions of different organic compounds

1.1 Introduction to Organic Chemistry

Organic compounds tend to be molecular

Mainly composed of just six nonmetallic elements C, H, O, N, S, and P

Contains halides group- organohalides

Unique things about carbon atom - can form four bond - bond is very strong and nonreactive - can form long chains - can form rings - bond formed with single, double, or triple

bonds


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Properties Compounds found in all three states

- solids, liquids, and gases - solids tend to have low melting points

Solubility in water varies depending on which of the other elements are attached to C and how many there are - CH3OH is miscible with water; C10H21OH is insoluble

Hydrophobic part


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Bonding and Hybridization


sp3

When C has four single bonds, the shape is tetrahedral, carbon sp3

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sp2

When C has two single + one double bond, the shape is trigonal planar, carbon sp2

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sp

When C has one triple + one single or two double bonds, the shape is linear, carbon sp

Structural Formulas of Organic Molecules

Molecular Formula tells us what are the elements and how many atoms of each element are present in one molecule

For example C2H7N C3H8O

Structural Formulas of Organic Molecules

Structural Formula tells us the actual number of atoms and shows the order in which the atoms in the molecule are connected together

For example C2H7N and C3H8O

C C NH

HH

H

H

HH C N C

H

HH

H HH

HFormula I : Ethanamine Formula II : Dimethylamine

C C CH

HH

H

H

HO

HH C O C

H

HH

HC

HH

H

HFormula I :1-Propanol Formula II : Methoxyethane

Ways of Depicting the Organic Molecules

Expanded structural formula shows every atom and type of covalent bond in the molecule

C C CH

HH

H

HO H

OC CH

HH

HCH

HC CH

HH C C

H

HH


Condensed structural formula shows every atom and type of covalent bond in the molecule

C C CH

HH

H

HO H

O

C CH

HH

HCH

CH3CH2COOH

C C CH

HH

H

H

H

HCH3CH CH(CH2)2CH3


Skeletal structural formula shows the carbon skeleton, the atom hydrogen omitted on carbon, unless hydrogen bound to the heteroatoms.

C C CH

HH

H

H

HN

C C CH

HH

H

HO H

O

C CH

HH

HCH

CH

H

O

OH

NH2

H

H

HH

CC C

CC

H OHH

H HH

H

HHH

OH


Skeletal structural formula in 3D 3D geometry of atoms spatial arrangements of atoms or groups of atoms within the molecule. Wedges and dashes to indicate 3D Cl

OH

Cl

HO

Cl

HO

wedge represent a group coming out of the planeof paper

dash represent a groupgoing behind of the plane of paper

solid line represent a grouplying in the plane of paper

Exercise 1 : Write the expanded structural and condensed formula for the straight chain alkane C8H18

Exercise 2 : Write the molecular formula and condensed structures for each of the following compounds

Exercise 3 : Write the carbon skeletal for compounds below

CH3CH2CHCHCCH2COOH

Br

OH

Primary carbon one alkyl group and three atoms hydrogen

Secondary carbon two alkyl groups and two atoms hydrogen

Tertiary carbon three alkyl groups and one atom hydrogen

Quarternary four alkyl groups and no atom hydrogen

Classification of Carbon and Hydrogen Atoms in Organic Molecules

Primary hydrogen three atoms hydrogen attached to primary carbon

Secondary hydrogen two atoms hydrogen attached to secondary carbon

Tertiary hydrogen three atoms hydrogen attached to tertiary carbon

Classification of Carbon and Hydrogen Atoms in Organic Molecules

Exercise 4 : Identify the carbon atoms in the following molecules as primary, secondary, tertiary or quaternary

CH3CHCH2CCH3

CH3

CH3CH3

(a) (b)

Exercise 5 : Identify the hydrogen atoms on the above molecules as primary, secondary, or tertiary

Functional groups is a group of atoms that have a chemical behaviour of the parent molecule.

is the structural unit responsible for a given molecules reactivity under a particular set of conditions.

The group reacts in a typical way, generally independent of the rest of the molecule

Functional Groups and Homologous Series

Functional Groups

Class Functional Group Example

Alkene C C

CH3

H3C CH2Limonene


Alkyne


Norethindrone

C C

O

COH CCH3

H

Functional Groups



Alkyl HalideX = F, Cl, Br, I

R X

ClCl

ClCl

Cl

Cl

1,2,3,4,5,6-Hexachlorocyclohexane Lindane

Functional Groups



Alcohol R OH

CH3

H3C CH3

OH

2-Isopropyl-5-methylcyclohexanol Menthol

Functional Groups


OH3C CH3

(CH2)4CH3HO

H3C

'9-Tetrahydrocannabinol THC


Ether R O R'

Functional Groups



Aldehyde

Cinnamaldehyde

OC

R H

CC

CO

H

H

H

Functional Groups



Ketone

Jasmone

CH3

CH3

OOC

R R'

Functional Groups



Carboxylic Acid

Ibuprofen

OC

R OHC

CH3

CH3

CH3O

OH

Functional Groups


EsterOC

R OR'

CO

OCH3

OH


Methyl salicylate

Functional Groups



Amine

Mescaline

NR R' R"

NH2

OCH3H3CO

H3CO

Functional Groups


Differences between functional groups and class of compound they are not the same!

For example : 2-butanol functional group is (-OH) hydroxyl group .But the class of the compound is alcohol.


CH3CH2CHCH3OH

Differences between functional groups and class of compound they are not the same!

For example : Propanal and propanone functional group is (C=O) carbonyl group. But the class of the compound is aldehyde and ketone respectively


H3CH2CC

H

O

H3CC

CH3

O

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Exercise 6: i) Draw any three chain isomers of C7H16 ii) Draw any two positional isomers of C5H12O iii) Draw any one functional isomers of C5H12O

Homologous series a series of organic compounds with similar chemical properties, in which each member differs from previous one by the addition of a CH2- group is called a homologous series

The members of a homologous series are called homologues.


General properties - same functional groups and similar chemical

properties - each member differs from next in the series

by a CH2 group - can be prepared by similar methods - physical properties is progressive change

with increasing molecular mass - contain the same elements and represented

by the same general formula


General formula - a general formula is a formula that can apply not only to a specific compound but to all compound in the same homologous series.

Some homologous series have the same general formula

- Alkenes and cycloalkanes (CnH2n) - Alkynes and cycloalkenes (CnH2n-2) - Aldehydes and ketones (CnH2nO) - Carboxylic acids and esters (CnH2nO2)


Homologous series

General Formula

Example Structural Formula

Alkanes CnH2n+2 C6H14 CH3(CH2)4CH3 Alkenes CnH2 C6H12 CH3(CH2)3CH=CH2 Alkynes CnH2n-2 C3H4 CH3C{CH Haloalkanes CnH2n+1X C3H7 Br CH3CH2CH2Br

Alcohols CnH2n+2 O C3H7 OH CH3CH2CH2OH

Aldehydes CnH2n O C4H8 O CH3CH2CH2CH=O

Ketones CnH2n O C4H8 O CH3CH2C=OCH3 Carboxylic acids CnH2n O2 C3H6 O2 CH3CH2COOH

Esters CnH2n O2 C3H6 O2 CH3COOCH3 Amine CnH2n+1NH2 C3H7 NH2 CH3CH2CH2NH2


Isomerism - two or more organic compounds with same molecular formula but different arrangements of atoms in space within the molecules.

Two main types Structural or constitutional isomerism Stereoisomerism

Isomerism in Organic Molecules

See page 77 - 81

Isomerism

Constitutional

Isomerism

Chain

Isomerism Positional Isomerism

Functional Isomerism

Stereoisomerism

Geometrical Isomerism

Optical Isomerism


Constitutional or Structural isomerism - molecules have same molecular formulae but different structural formulae

Divided into three types


See page 77 - 81

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Constitutional Isomerism

Divided into three types i) Chain isomers - different structural formulae due to

varying lengths in its carbon chains or carbon skeletons. The length of carbon chains can be altered due to branching.

n-butane (Unbranched) Isobutane

(Branched chain)

C C C C HH

H

H

H

H

H

HH

H C C C HH

HH

HH

H

CHH

H

See page 77 - 81


ii) Positional isomers - molecules have same carbon chain and functional groups but differ in the position of the functional group


C C C C BrH

H

H

H

H

H

HH

HC C C C H

H

H

H

H

Br

H

HH

HBromobutane 2-Bromobutane

See page 77 - 81


iii) Functional isomers - molecules have different functional groups, hence their structural formulae are different.


C C C HH

H

HH

HC C C H

H

H

HH

H

O O

Propanal Propanone

See page 77 - 81


Possible structural isomers of alkanes


Carbon Chains

Molecular Formula Possible Isomers

4 C4H10 2

5 C5H12 3

6 C6H14 5

7 C7H16 9

8 C8H18 18

9 C9H20 35

10 C10H22 75

Rotation about a bond is NOT isomerism


See page 77 - 81

Stereoisomerism - molecules have same molecular formulae and structural formulae but different orientation of atoms and bond in space within the molecules


Divided into two types Geometrical isomers have the same

molecular formula but a different orientation in space that cannot be overcome by rotation around a sigma bond

Geometric isomers occurs if the presence of a carbon-carbon double bond or a ring structure in its molecule

Double bond between two carbon atoms, the central sigma bond is sandwiches by a pi bond above and below. This pi bond prevents the rotation of the carbon atoms.


Geometrical isomers


C CH

H3C CH3

HC C

H3C

H CH3

HCis-2- butene Trans-2- butene

H3C

HH

CH3

HH

H3C

HH

H

CH3

H

Cis-1,2-dimethylcyclopropane Trans-1,2-dimethylcyclopropane

Optical isomerism is shown by an organic compound which has a chiral carbon atom in its molecules

A chiral carbon atom is a carbon atom which has four different atoms or groups of atoms attached to it.

A chiral carbon also known as an asymmetric carbon, the molecule would have a mirror image that cannot superimposed on it. A chiral molecule and its mirror image are called enantiomer


Optical isomerism


CCH3

OHC2H5 C

CH3C2H5HO HH

I I I I I I I I

Covalent bond cleavage during reaction, chemical bonds have to be broken in order that new compounds may be formed

Breaking the chemical bonds is called fission

Bond breaking or formation can be symmetrical or unsymetrical

Symmetrical bond breaking homolytic fission

Unsymmetrical bond breaking heterolytic fission

Introduction to Organic Molecules Reactions

Homolytic fission two shared electrons of the covalent bonds are split equally.

The resulting species are known as free radical

Heterolytic fission two shared electrons of the covalent bonds are remain one one of the atom

The resulting species known as carbonium ion


A B. . A. B.+

A B. . A+ B-+ ..

Carbonium ions there are two species carbocation and carbanion

Carbocation is an organic ion which contain a carbon atom with a positive charge

Carbanion is an organic ion which contain a carbon atom with a negative charge


CHH

HC+HH

H+ Cl-Cl

Methyl chloride Methyl carbocation

CHH

HC-HH

H+ H+H ..

Methane Methyl carbanion

Curved arrows - indicate breaking and forming of bonds

Arrowheads with a half head (fish-hook) indicate homolytic and homogenic steps (called radical processes)

Arrowheads with a complete head indicate heterolytic and heterogenic steps (called polar processes)


Nucleophile (Nu-) - is a species (ion or molecule) which attacks electron-poor carbon atom of organic molecule, by donating electron-pair to the atom.

Nucleophiles are Lewis bases, containing lone pair of electrons

Examples: CN-, OH-, Br-, I-, OCH3-, H2O, NH3, CH3NH2,


Electrophile (E+) -is a species (ion or molecule) which attacks electron-rich site of organic molecules such as double bonds.

Electrophiles are Lewis acids (either positive ions or molecules with electron-deficient atom)

Examples: HCl , H3O+, AlCl3, BF3, Cl2, Br2,FeCl3, ZnCl2


Mechanism - describes the steps behind the changes that we can observe

Reactions occur in defined steps that lead from reactant to product

We classify the types of steps in a sequence A step involves either the formation or breaking

of a covalent bond Steps can occur in individually or in

combination with other steps When several steps occur at the same time they

are said to be concerted


Main types of reactions Addition Electrophile or Nucleophile

reactions Elimination reactions Substitution Nucleophilic Substitution Rearrangement reaction


Addition Electrophile or Nucleophile reactions two reactants added together to form a single product

Elimination reactions single reactant splits into two products


C C + X Y C CX Y

C O + Nu- CNu

OH

Electrophilic addition Nucleophilic addition

C CX Y

C C + X Y

Substitution or Nucleophilic substitution reactions two molecules/atoms exchange parts

Rearrangement reactions a molecule undergoes changes in the way its atoms are connected


C CY

+ Nu- C CNu

+ Y

C C CCC C CC

Checkpoint 1

OO

HOO

CH3 OHCH3

O O

CH3

H3C

CH5C6

O C CH3O

CNCH5C6

OO C6H5

OHHO

CO

H3C

Circle the functional groups present in this molecule

Checkpoint 2 Draw the skeletal structure for each of the following compound

C

CC

C

CC

H

H

H H

H

H

H

H

H

OH

H3CCH

CH

CH3

C

OH

N C

CN

C

CC H

H

H

H

H

Checkpoint 3 1. Draw all chain isomers with a molecular formula C7H16 2. Draw the functional groups isomer for the following compounds a) CH3CH2CH2CH=CH2 b) CH3CH2COOH 3. Draw the positional isomer for the following

compounds a) CH3CH(OH)CH2CH2CH3 b) 1,2- Diethylcyclohexane

Checkpoint 4 1. Draw the stereoisomer for the following

compounds a) CH3CH2CBr=CHCH3 and b) 1,4 Dichloropentane 2. Which of the following compounds exhibit

the optical active? Draw the diagram to show the optical isomer that may exist for the particular compound.

a) (CH3)2C(NH2)(COOH) b) CH3BrCHOH

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