Introduction to Organic Chemistry (LEC)

Question 1

What is Organic Chemistry?

Answer 1

It is the chemistry of hydrocarbons (hydrogen + carbon compounds) and their derivatives

Question 2

Organic compounds are classified as either:

Answer 2

• Hydrocarbons
• Derivatives of hydrocarbons

Question 3

What is the Vital Force Theory?

Answer 3

Held that organic substances could only originate from living material (eg plants, animals).

No organic compounds could be formed without the aid of a vital force supplied by living cells.

Question 4

How was the Vital Force theory overthrown?

Answer 4

A scientist named Wohler made NH2CONH2 from NH4OCN, an inorganic compound.

NH2CONH2 - urea
NH4OCN - ammonium cyanate

Question 5

Sources of Organic Compounds:

Answer 5

1. Animals - Fats, proteins
2. Plants - Starch, cellulose
3. Wood - Wood alcohol, acetone, acetic acid
4. Natural Gas - Methane
5. Coal - Coal tar, drugs, benzene, phenol
6. Petroleum - Gasoline, kerosene, fuel oils
7. Fermentation processes - Ethyl alcohol, acetone
8. Laboratory synthesis

Question 6

Elements that make up organic compounds:

Answer 6

• C
• H
• O
• N
• P
• S

Halogens:
1. At
2. Br
3. Cl
4. F
5. I
6. Ts

Question 7

Characteristics of Organic Compounds:

Answer 7

• Low boiling & melting points
• Low solubility in water
• High solubility in nonpolar solvents thus nonconductors of electricity
• Covalent bonding thus rarely ionize
• Less reactive
• Flammable, thus less stable towards heat
• Exhibit isomerism

Question 8

The phenomenon of two or more compounds having the same molecular formula but different structural arrrangements is called:

Their individual compounds are called:

Answer 8

Isomerism; Isomers

Question 9

Carbon’s unique character is attributed to:

Answer 9

• Position in periodic table
• Ability to bond with itself to form multiple bonds

Question 10

Carbon’s position in the periodic table:

Answer 10

• Middle of the second period
• Atomic number: 6
• Has 6 valence electrons: 2 in first shell, 4 in outer shell for bonding purposes

Question 11

Why is it energetically unfavorable for carbon to gain (C^-4) or lose 4 (C^+4) electrons for rare gas configuration?

Answer 11

Due to its position in the periodic table, C is neither strongly electronegative nor electropositive and has little tendency to form (C^-4) or (C^+4).

Question 12

How does C bond with other elements?

Answer 12

By sharing electrons (covalent bonding) and attaining inert gas configuration.

Question 13

What makes carbon responsible for its large number of compounds?

Answer 13

Catenation, the ability of an atom to bond to itself to form chains and rings.

Question 14

Electron structure of C:

Answer 14

1s^2 2s^2 2p^2

Question 15

How does C atom form 4 equivalent bonds:

*(page 4)

Answer 15

Prior to change: 1s^2 2s^2 2p^2

1. 2s electron is promoted to a 2p orbital
2. Outer shell structure becomes 2s^1 2px^1 2py^1 2pz^1
3. These then hybridize to form 4 equivalent hybrid sp orbitals.
4. Four sp^3 orbitals are formed, each containing one electron.

= 2sp^3

Question 16

What types of bonds can C atoms form?

Answer 16

Covalent bonds
- Single bond (one pair)
- Double bond (two pairs)
- Triple bond (three pairs)

Question 17

Formula that represents an entire series of compounds

Answer 17

General formula

Question 18

Formula that gives the actual/total number of atoms of the constituent elements in the molecule

Answer 18

Molecular formula

Question 19

Formula that shows the arrangement of the atoms or groups of atom in the molecule

Answer 19

Structural formula

Question 20

Formula that shows all the bonds of the atoms in the molecule

Answer 20

Graphical formula

Question 21

Formula that implies carbon atoms at the corners and ends of lines

Answer 21

Line-Angle Formula

Question 22

It is the portion of the molecule that is highly reactive and which therefore participates most readily in chemical reactions.

Answer 22

Functional groups

Question 23

Each class of compounds exists as a homologous series that exhibits __________ as a result of having a common functional group.

Answer 23

Similar chemical properties

Question 24

In the analysis of organic compounds, the first step involved is:

Answer 24

Purification - the physical separation of a chemical substance of interest from foreign or contaminating substances.

Question 25

Method of purification wherein the substance is dissolved in a solvent and again put in cystalline form under conditions which ensure greater purity.

Answer 25

Crystallization (Recrystallization)

Question 26

What make a solvent suitable for crystallization?

Answer 26

Compound shows high solubility when hot, but only moderate solubility when cold.

Therefore when hot solution cools, crystals deposit

Question 27

Method of purification wherein two solvents (usually water & chloroform) are used. Chloroform must dissolve solute more freely than water, and be immiscible with water.

Answer 27

Extraction with an immiscible solvent​

Question 28

Method of purification wherein substance does not liquify, but passes directly from:

• Solid to gas when heated
• Vapor to solid upon cooling

Answer 28

Sublimation

Question 29

Method of purification with the process of heating an impure liquid to gas, and then cooling the gas to condense it back to liquid.

Answer 29

Distillation

Question 30

Distillation results in separation of impurities from a sample because of differences in the _____

Answer 30

Boiling points

Question 31

The purity of a known organic compound is established by determining that its physical constants are:

Answer 31

Identical with those already recorded in the literature for that compound.

Question 32

It is defined as the temperature at which solid & liquid forms exist in equilibrium with each other atmospheric pressure.

A pure compound gives:

Answer 32

Melting Point; sharp, constant melting points

Question 33

It is the temperature at which the vapor pressure is equal to the external pressure.

If volatile impurities are present, they will _____ with the pure substance when mixture is boiled.

Answer 33

Boiling point; vaporize

Question 34

Detection of C:

Answer 34

Charring or heating

• Blackening of substance always indicates the presence of organic compounds.

With concentrated sulfuric acid

• Carbonization results when concentrated sulfuric acid is added to an organic compound.

Question 35

Detection of N:

Answer 35

Burnt hair or feather odor

• When an organic compound is heated alone and it gives an odor of a burnt hair or feather

Soda-lime process (NaOH + CaO)

• Some organic compounds which contain nitrogen when heated with soda-lime gives a gas with urine-like odor, and turn wet red litmus paper to blue. This gas is ammonia.

NH2CONH2 (Urea) + NaOH (Soda lime) + CaO = NH3 (Ammonia)

Question 36

Detection of S:

Answer 36

Lead acetate test

• A portion of the solution is treated with lead acetate. The formation of a black precipitate of lead sulfide indicates presence of sulfur.

Question 37

Detection of P:

Answer 37

Phosphorus in the organic compound is oxidized to phosphate by fusing with potassium nitrate—sodium carbonate mixture dissolved in water and tested with

Ammonium molybdate test
- Formation of yellow crystalline precipitate indicates presence of P.

Question 38

Detection of Halogens:

Answer 38

Beilstein test

• Halogen in an organic compound can be detected by heating the compound on a clean copper wire in the Bunsen flame. The presence of a halide is shown by a green flame, caused by the decomposition of copper halide which has been formed.

Carbon tetrachloride

• Acidified potassium permanganate is added to the stock solution. Then carbon tetrachloride is added and layers are formed:

Iodine: Purple
Bromine: Orange
Chlorine: Colorless