CHEM-103
UNIT- 01
Organic Chemistry
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Definition of Organic Chemistry: Organic compounds are those which contains carbon
(C) as their main constituent atom. Hydrogen (H) is another must constituent atom for
the formation of any organic compounds.
Chemistry, that deal with carbon containing
compounds are known as organic chemistry. Because of carbon and hydrogen is the
must constituent atom for any organic compounds so they are also called as
hydrocarbon.
Difference between Inorganic and Organic chemistry:
Inorganic chemistry
Organic chemistry
1. Inorganic compounds are normally 1. Organic compounds are normally soft;
solid, hard and shiny.
almost stay in liquid as well as in gaseous
form.
2. Inorganic compounds are ionic 2. Organic compounds are covalent bonded
bonded compounds.
compounds.
3. Inorganic compounds contain higher 3. Organic compounds contain comparatively
melting and boiling point.
lower melting and boiling point.
4. Inorganic compounds can conduct 4. Organic compounds can not conduct
electricity.
electricity.
5. Inorganic compound can not form 5. Organic compounds stay in molecular
molecule.
form.
6. Example: H2O, H2SO4 etc.
6. Example: CH4, C6H5-OH etc.
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Q: Why CH4 is the first organic molecule not CH2? Or
Q: Discuss the sp3 hybridization in methane (CH4) molecule? Or
Q: Discuss sp3 hybridization with examples.
Ans: The first molecular formula of organic compounds is methane (CH4). The ground
state electronic configuration of carbon atom is,
C (6): 1s2 2s2 2px1 2py1 2pz0
; shown in fig: 1(a)
Where will find that, carbon atom has only two unpaired electron. So, carbon atom can
form only two covalent bonds. If it would true then the first molecular formula of
organic compound would CH2 but we know that the first molecular formula of organic
compound is CH4. In excited state electronic configuration of carbon atom is,
*C (6): 1s2 2s1 2px1 2py1 2pz1
Where we find that, one of the 2s orbital, electron jumps to the outermost higher
energy shell 2pz.
: shown in fig: 1(b). So, from the excited state electron
configuration of C-atom, it founds that C-atom gains four unpaired electron shell. So,
C-atoms valency is four. Thus, it requires four other electrons to take part in chemical
reaction.
During the formation of CH4 molecule C-atom shared its four outermost
electrons with four H-atoms. Thereby, four C-H covalent bond forms. C-atom uses its
sp3 hybrid orbital and H-atom uses its s-orbital. So the bonding between C-H is sp3-s.
For this reign, CH4 molecule C-atom is in sp3 hybridized.
; shown in fig: 1(c)
Hybridization state:
2s
2px 2py 2pz
Hybridization
2p
2px
2py
2pz
2px
2py
2pz
2(sp3)
2s
2s
2s
1s
1s
1s
Fig: 1(a) Ground state
electronic configuration of
C-atom.
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2p
Fig: 1(b) Excited state
electronic configuration of
C-atom.
Fig: 1(c) Hybridized state
electronic configuration in
CH4 molecule.
Homologous series:
1. All the compounds belong to a family can be shown by a general molecular formula.
Example: Alkane → CnH2n+2
Alkene → CnH2n
Alkyne → CnH2n–2
Alcohol → CnH2n+1OH
2. In a series of a family member the different in molecular formula is a same unit i.e.
–CH2, between two nearest members.
Example: Methane – CH4 CH2
Ethane – C2H6
CH2
Propane – C3H8
Butane – C4H10 CH2
Pantane – C5H12 CH2
Hexane – C6H14 CH2
3. All the family members in a family follow a general preparation method for their
production.
4. All the family members having almost the same physical and chemical properties.
5. The source of all the family members is same.
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Isomerizm: Compounds having the same molecular formula but different in their
structures formula are isomers of each other and the process is known as Isomerizm.
Example: C4H10
H
H H
H
H–C–C–C–C–H
H H
H H
n-butane
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H CH3 H
H–C–C–C–H
H
H H
2-methyle propane
IUPAC: (International Union for Pure Applied Chemistry) (That was done in class)
Types of Hydrocarbon: Hydrocarbons are classified in two main types according to
their bonding in the molecule.
a) Saturated Hydrocarbon
b) Unsaturated Hydrocarbon.
a) Saturated Hydrocarbon: In these types of compound the central C-atoms are fully
saturated with H-atoms. It means C-atom satisfy its four valences with four H-atoms
resulting four covalent bonds (σ-bond). In a long chain of hydrocarbon C-atom satisfy
its valences with H-atoms as well as with adjacent C-atom. Saturated hydrocarbons are
single bonded compound.
Example: CH4, C2H6, C3H8, C4H10 etc.
b) Unsaturated Hydrocarbon: In these types of hydrocarbon, carbon skeleton is not
fully bonded with H-atoms thus not satisfied with four simple covalent bonds (σ-bond).
C-atoms are occupied with free unpaired electrons. Those similar unpaired electrons of
two adjacent carbons make side to side overlapping which results π-bond.
Example: C2H4 (Ethylene), C2H2 (Acetylene) etc.
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Electro negativity: The tendency of an atom to attract electrons towards it self is known
as electro negativity. It is the general characteristic of non-metallic atom.
Polar bond: when a covalent bond form between two atoms or different electro
negativity then the more electro negativity atom attaches the sharing electrons towards
him more then the less electro negativity atom. Thus the electron density becomes
more around it so it gains small negatively charged body (δ–). On the other hand his
sharing other partner due to less electron density becomes small positively charged
body (δ+). If there is a positive and negative end in a covalent bond is known as polar
bond.
Example: C-Cl covalent bond is a polar bond.
Cl δ–
.


C δ+
Fig: C – Cl covalent bond.
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Non-polar bond: When a covalent bond forms between two atoms of similar electro
negativity then the electron density around the both atom is same. There is no positive
or negative end as in the polar bond. This type of covalent bond is known as non-polar
bond.
Example: In chlorine molecule (Cl2) the (Cl – Cl) covalent bond is a non-polar covalent
bond.
Cl
.


Cl
Fig: Cl – Cl covalent bond.
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Q: Which one is more reactive between CH3 – CH2 – CH3 and CH3 – CH2 – CH2Cl?
Ans: Between these two compounds first one is propane and second one is
choloropropane. In choloropropane there is a covalent bond between two different
electro negativity atoms Cl and C. The electron density is not equal around both the
atoms. C-atom is less electro negative. So the electron density around Cl-atom is higher
then C-atom. Thus, a positive charged end (δ+) exists in C-atom and Cl-atom remains
with negative end (δ–). This fact results a polar bond between C and Cl. Due to the
presence of positive and negative end polar bond can break easily resulting active free
radical for chemical reaction. Because the presence of polar bond in choloropropane is
more reactive then propane as there is no polar bond (only non-polar bond) in propane.
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Bond Dissociation Energy: The amount of energy is required or liberated during a
chemical bond breaking. The amount of energy is known as bond dissociation energy.
It is shown by D.
Example:
∙
∙
∙
∙
CH4 → CH3 + H (CH3 – H, D = 104 Kcal/mol)
CH3 → CH2 + H (CH2 – H, D = 106 Kcal/mol)
∙
∙
CH2 → CH + H
(CH – H, D = 106 Kcal/mol)
∙
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CH → C + H
(C – H, D = 84 Kcal/mol)
Types of Bond Dissociation: Bond dissociation are two types,
a) Homolytic bond dissociation and
b) Heterolytic bond dissociation.
a) Homolytic bond dissociation: When a covalent bond forms between two equal
electronegative or electropositive atoms then the electron density around both the
atoms remain same. During their bond breaking both the bonded atoms takes up their
respective atoms. Thus, both the atom becomes neutral three radicals.
A
‫׃‬
∙
∙
∙
∙
B → A + B [When A and B is free radical]
b) Heterolytic bond dissociation: When a covalent bond forms between two atoms of
different electronegativity then the electron density differs around both atoms. Electron
density is higher around more electronegativity atom and less around less
electronegativity atom. During their bond dissociation the sharing electron distribution
is unequal. The more electronegativity atom takes up both the sharing electron
resulting negatively charged free radical and the bonded other atom becomes positively
charged free radical. This type of bond dissociation is known as heterolytic bond
dissociation.
A ‫ ׃‬B → Aδ+ + ‫ ׃‬Bδ–
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Acid-Base:
Q: Why CH3COOH is a weak acid?
Ans:
CH3COOH → CH3COO– + H+
Acidity of any acid depends upon its ionization capacity. In the above example of the
CH3COOH ionization, only one of the four H-atoms goes into the aqua’s solution as Hion (Proton). Three other H-atoms are satisfying the carbon valences. So, they can not
go to the solution as proton. The ionization percentage of CH3COOH is 0.4%. So,
CH3COOH is a weak acid.
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