Chapter#1.5 Introductory Organic Chemistryy

H. M. Sulman Munir ([email protected]) Bright Future Pakistani Intr. SchoolO / A Level Chemistry Teacher Doha, Qatar

Introductory Organic Chemistry

The word ‘organic’ is actually derived from the word organism but in modern chemistry its

definition is:

“The study of hydrocarbons and their derivatives is called organic chemistry.”

CO, CO2, metal and ammonium cyanides, carbonates and metal carbonates are not

organic compounds even they contain carbon.

The difference between hazard and risk:

“Hazard is the potential of a substance to do harm”. It is an absolute and fixed property of

a substance. e.g if a substance is poisonous or carcinogen.

“Chance or extent of the harm from a hazard is called risk”.

Risk depends upon:

(1) The nature of hazard

(2) The level of exposure e.g a poisonous substance if coming into contact, it is the risk: It

depends upon

(a) the expertise of the person working

(b) the amounts of the hazardous substances being used.

(c) conditions which can affect hazard level of a substance

The level of risk can be minimized by using protective clothing or better equipment.

(1) e.g keep combustible (hazard) material away (minimizing) from fire or flame.

(2) If a substance is poisonous use gloves, mask or gas mask (if gas is involved), fume cup-

board, goggles.

(3) Use minimum possible amounts or concentrations of the hazardous substances. As dilute

acids cause less harm than the concentrated ones.

Structural basis of organic compounds:

Carbon is the base of organic compounds. It makes four

covalent bonds (single, double or triple) because its

outermost shell contains four electrons.

Other important is H which has valency 1 and always a single covalent bond. Fig. above

shows the simplest structure (Dot and Cross model of methane) of organic chemistry.

Families (homologous series or classes) of organic compounds:

In organic chemistry many organic compounds have the same chemical properties;

compounds having the same chemical properties are classified in a group called the

homologous series.

The similarity in chemical properties is due to same functional group.

Notes Chapter 1.5 (Introductory Organic Chemistry) ‘AS’ Level 1

H. M. Sulman Munir ([email protected]) Bright Future Pakistani Intr. SchoolO / A Level Chemistry Teacher Doha, Qatar Functional group:

“An atom, group of atoms and some

double or triple covalent bond which is

responsible for the characteristic chemical

properties of the organic compounds is

called functional group.”

Some important terminology:

Aliphatic: Non-cyclic organic compounds

e.g propane, butane

Alicyclic: closed chains or rings of carbon

atoms. eg cyclohexane

Arenes: Benzene (a ring containing six

carbon atoms and special type of double

covalent which is called delocalized) and

its derivatives.

Representing the organic compounds: (formulae expressions of different types)

1. Molecular formula : it tells us the total number of atoms of each element separately.

e.g butene (C4H8), Butanoic acid (C4H8O2)

2. Empirical Formula : It tells us the simplest whole number ratio of the atoms of different

elements in a compound. Butane (CH2), butanoic acid (C2H4O).

3. Structural formula : it tells us the groups of atoms which are together.

Butane (CH3CH=CHCH3 or CH3CH2CH=CH2), Butanoic acid (CH3CH2CH2COOH)

4. Displayed formula : it shows all the covalent bonds of a molecule.

5. Skeletal Formula : it’s a zig-zag arrangement of carbon atoms and hydrogen attached to

them but these are not shown by C or H respectively.


H. M. Sulman Munir ([email protected]) Bright Future Pakistani Intr. SchoolO / A Level Chemistry Teacher Doha, Qatar 6. Three dimensional (3D) formula : All of the four single covalent bonds are not in the

same plane. The two in the same plane are shown solid lines, one out of the plane is

shown by a wedge and one into the plane is shown by dotted line.

Note: While writing the formulae of organic compounds, read the question carefully. You

may lose marks if you are writing displayed and requirement is structural etc.

Question: like carbon, silicon also forms four covalent bonds. Why it does not make variety of

compounds.

Answer: Si-Si and Si-H bond energy is very low as compared C-C and C-H bond energy respectively

because the bonds formed by silicon are longer bonds. So the bonds of Si are unstable and weaker.

Nomenclature (naming) the organic compounds:

First of all memorize what word will be used for the number of carbon atoms in a molecule.

No. of C-atoms in the chain Root word used No. of C-atoms in the chain Root word used

1 meth 6 hex

2 eth 7 hept

3 prop 8 oct

4 but 9 non

5 pent 10 dec

Families:

1. Alkane: Root word + ane prop + ane (propane)

2. Alkene: Root word + ene prop + ene (propene)

3. Alcohols: alkan + ol (remove e of alkane) ethan + ol (ethanol)

4. Carboxylic acid: alkan + oic acid (remove e of alkane): propan + oic acid (propanoic acid)

5. Aldehydes: alkan + al (remove e of alkane) propan+ al (propanal)

6. Ketones: alkan + one (remove e of alkane) propan + one (propanone)

Nomenclature of alkanes:

There is a sequence of some steps for writing the names of organic compounds. Other

families have bit changes in the rules used for alkanes.


H. M. Sulman Munir ([email protected]) Bright Future Pakistani Intr. SchoolO / A Level Chemistry Teacher Doha, Qatar 1. Select the longest possible chain containing all the carbon atoms attached to the functional

group. The number of carbon atoms in the chain gives the ending word as alkane.

2. Assign a number to each carbon of the chain starting from the end which gives least

possible number to the carbon atoms which are branched.

3. Write the number to which the branch is attached, a hyphen (-) then name of the branch

and at the end name of the chain as an alkane.

4. If more than one branches which are different, write their names alphabetically.

5. If branches are same write and repeat the number for each branch and before the name of

the branch show number of branches by words like di (for two), tri (for three) etc.

6. If chains of same lengths are possible but number of branches is different, choose a chain

with more number of branches.


H. M. Sulman Munir ([email protected]) Bright Future Pakistani Intr. SchoolO / A Level Chemistry Teacher Doha, Qatar Q-1 (a) Write down the names of following organic compounds according to IUPAC system and draw their skeletal formulae.i. CH3CH2CH(CH2CH3)CH2CH3 ii. (CH3)3CCH2C(CH3)3

iii. CH3CH2C(CH3)2(CH2)2CH3 iv. (CH3CH2)3CH(b) Write the structural formulae of the following compounds.i. 4-ethyl-3,4-dimethylheptane ii. 2,2,3,4-tetramethylpentaneNomenclature of alkenes:

1. Select the longest chain containing all the carbon atoms which are double bonded.

2. Name the branches as we did in alkanes.

3. Parent name: root word then hyphen position of the double bond and then ene, diene,

triene etc.

CH2=CHCH2CH3 (but-1-ene) CH3CH=CHCH3 (but-2-ene)

CH3CH2C(CH2CH3)C(CH3)2 it can be shown in open form as

Q-2 Write IUPAC names of the following compounds.

(a) CH2=C(CH2CH3)CH2CH2CH3(b) CH3C(CH3)C(CH3)CH(CH2CH3)CH2CH3

(c) CH2=CHCH=CHC(CH3)CH2 (d) C(CH3)3CH=CHC(CH3)3

Q-3 For this question use the information about “families”.

Write IUPAC names of the following organic compounds.

(d) CH3CH2CH(OH)CH3 (e) CH2(OH)CH2(OH)(f) CH3CH(OH)2

Note: These compounds having chains of carbon atoms are called aliphatic compounds,

some have rings are called alicyclic and some have a special type of ring (benzene) are

called arenes.

Note: In this chapter we will study structural isomerism and its types in detail, EZ (cis-trans)

isomerism will be covered in chapter#1.7 and optical isomerism in A2.

Isomerism: The study in which more than one compounds have same molecular formula

but different structural formulae or some different physical property is called isomerism.


H. M. Sulman Munir ([email protected]) Bright Future Pakistani Intr. SchoolO / A Level Chemistry Teacher Doha, Qatar

(1) Structural isomerism: Compounds having same molecular formula but different

structural formulae are called structural isomers.

(a) Chain/skeletal isomerism: compounds having same molecular formula but different

number of carbon atoms in the chain selected are called chain isomers. These isomers

belong to same homologous series, so they have same chemical properties but different

physical ones.

C4H10: CH3CH2CH2CH3 (4 carbon atoms in the chain)

CH3CH(CH3)CH3 (3 carbon atoms in the chain)

Q-5 Draw displayed formulae of the three isomers of pentane, C5H12.

(b) Positional isomerism: Compounds having the same molecular formula but different

position of the branch or functional group are called positional isomers.

C6H14: CH3CH(CH3)CH2CH2CH3 (2-methylpentane)

CH3CH2CH(CH3)CH2CH3 (3-methylpentane)

Q-6 Draw positional isomers of

(a) C5H10 (both are alkenes) (b) C3H7Cl (c) C3H6Cl2 (it has four isomers)

(c) Functional group isomers: Compounds having same molecular formula but different

functional groups are called functional group isomers.

Sr

#

Molecular

formula

Functional group

of isomer 1

Isomer 1 Functional group

of isomer 2

Isomer 2

1 C3H8O C-OH

(alcohol)

CH3CH(OH)CH3

(propan-2-ol)

C-O-C

(ether)

H3C-O-CH3

(ether)

2 C5H10O

(aldehyde)

CH3CH2CH2CH2CHO

(butanal) (ketone)CH3CH2CH2COCH3

(butan-2-one)

3 C3H6O2

(carboxylic acids)

CH3CH2COOH

(propanoic acid)(ester)

CH3COOCH3 or

HCOOCH2CH3

Note: so this isomerism comes in pairs of homologous series like alcohol-ether, aldehyde-

ketone and carboxylic acids and esters.


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Chapter#1.5 Introductory Organic Chemistryy