Introduction To Organic Chemistry

Question 1

Why are there so many organic compounds?

Answer 1

Carbon forms strong bonds to other carbon atoms.
Organic compounds tend to be kinetically stable: there are large activation barriers associated with their reactions so the reactions tend to be slow, or require strong heat, or strong reagents to get them going.

Question 2

What are the two parts of an organic compound?

Answer 2

An organic compounds can be considered to be made up of two parts: a hydrocarbon chain and a functional group.
Most of the reaction of an organic compound are reactions of functional group it contains.

Question 3

What is homologous series?

Answer 3

Compounds that contain the same functional group, and only differ in the length of carbon chain, they are said to belong in the same homologous series.

Question 4

List the names of functional groups, and names of the class of compounds that contain them.

Answer 4

Bromo (bromoalkanes)
Chloro (chloroalkanes)
Hydroxy (alcohols)
Carbonyl: aldehyde (aldehydes)
Carbonyl: ketone (ketones)
Carboxylic acid (carboxylic acid)
Ester (esters)
Acyl chloride (acyl chlorides)
Amide (amides)
Amino (amines)
Nitrile (nitriles)

Question 5

What are the different types of formulae used to describe organic compounds.

Answer 5

Empirical formula; simplest ratio of elements the compound contains.
Molecular formula; tells us the number of atoms of each element that are in one molecule of the compound.
Structural formula; indicates which atoms are joined to which molecule of the compound.
Displayed formula; Shows all bonds and atoms within a molecule of a compound.
Stereochemical formula; is a displayed formula that shows the three dimensional shape of the molecule.
Skeletal formula; a simplified version of displayed formula, shows all the bonds in a molecule except those to hydrogen atoms, but omits all carbons and their attached hydrogen atoms.

Question 6

What is Isomerism?

Answer 6

Compounds with the same molecular formula but different arrangement of atoms.
There are two main types of isomerism; structural and stereo.
Structural isomers have different structural formula while stereo isomers have same structural formula.

Question 7

What are the types of structural isomers?

Answer 7

There are three types of structural isomers.
Chain isomers: have the same number of carbon atoms but different length of continuous carbon chain.
Positional isomers: Isomers with the same carbon backbone but different positions of the functional groups.
Functional group isomers: Contain different functional groups so they often have different reactions.

Question 8

How to determine functional group isomers?

Answer 8

If the hydrocarbon chain follows an alkane with one oxygen atom then the functional group isomers will be alcohol and ether.
If the hydrocarbon chain follows an alkene with one oxygen atom then the functional group isomers will be aldehyde and ketone.
If the hydrocarbon chain follows an alkene with two oxygen atoms then the functional group isomers will be carboxylic acid and ester.
All alkenes will have functional group isomers cycloalkanes except ethene.

Question 9

What are stereo isomers?

Answer 9

Isomers which have the same structural formula but different arrangement of atoms in space.
There are two types of stereo isomerism, Geometrical isomerism and optical isomerism.

Question 10

What is geometrical isomerism?

Answer 10

Geometrical isomerism or cis-trans isomerism occurs in alkenes that do not have two identical groups of carbon atoms attached on either end of the C=C double bond.
Unlike in C-C single bond it’s not possible to rotate one end of C=C double bond with respect to the other.
Compounds with both same groups on the same side of the plane are known as cis and the compounds with same groups across the plane are called trans.

Question 11

How to determine geometrical isomers?

Answer 11

If the ends of a hydrocarbon chain are different then count the number of double bonds and use the formula “2^n”, where n is the number of double bonds.
For geometrical isomerism in cycloalkene the ring must have minimum of 8 carbons, then we can use the formula “2^n”.

Question 12

What are optical isomers?

Answer 12

Light in which particles move in one direction is called plane polarised light.
Organic compounds which rotate PPL clockwise or anticlockwise are called optically active compounds.
An optically active compound and it’s mirror image are called optical isomers and they are non-superimposable.
* An optically active compound must have a chiral centre.

Question 13

What is a chiral centre?

Answer 13

A carbon attached to four different groups is called a chiral centre.

Question 14

What is meant by Dextrorotatory and Levorotatory?

Answer 14

Dextrorotatory rotates PPL clockwise while Levorotatory rotates PPL anticlockwise.
Mixture of 50% dextro and 50% levo is called a racemic mixture, and it is optically inactive.

Question 15

What are the differences in chemical and physical properties of optical isomers?

Answer 15

Optical isomers don’t have any difference in chemical or physical properties, they just rotate PPL in different ways.

Question 16

How to determine optical isomers?

Answer 16

Count the number of chiral carbons and use the formula “2^n” to find the number of optical isomers in a compound.
To find a chiral carbon don’t just see the adjacent.

Question 17

What is Heterolytic fission?

Answer 17

If a bond were to split unevenly (one atom getting both electrons, and the other none), ions would be formed. The atom that got both electrons would become negatively charged, while the other one would become positive. This is called heterolytic fission.

Question 18

What is Homolytic fission?

Answer 18

Homolytic fission is splitting a bond to produce two particles which are the same in the sense that they both have a single unpaired electron (both are free radicals).

To show that a species (either an atom or a group of atoms) is a free radical, the symbol is written with a dot attached to show the unpaired electron.

Question 19

What is an electrophile?

Answer 19

An electrophile is an atom or a group of atoms that reacts with electron rich centres in other molecules.
Electrophiles usually have an empty p orbital in their valance shell. They are either positively charged or have a S+ atom.

Question 20

What is a nucleophile?

Answer 20

A nucleophile is an atom or group of atoms that react with electron deficient centres in molecules. All nucleophile have a lone pair of electrons and many are anions.

Question 21

What is a radical?

Answer 21

A radical is an atom or group of atoms that has an unpaired electron. Radicals are sometimes called free radicals and are highly reactive.

Question 22

What is an addition reaction?

Answer 22

An addition reaction is one in which an organic molecule (usually containing a double bond) reacts with another to give only one product.

Question 23

What is a substitution reaction?

Answer 23

A reaction in which one atom or group replaces another atom or group in a molecule.

Question 24

What is an elimination reaction?

Answer 24

An elimination reaction is one that forms an alkene by the removal of H2O from an alcohol or a Br from a bromoalkane.

Question 25

What is a Hydrolysis reaction?

Answer 25

A reaction in which water reacts with a molecule and splits it into two smaller molecules.

Question 26

What is a condensation reaction?

Answer 26

A reaction between two molecules to form a larger molecule with the removal of a molecule of water.

Question 27

What is a reduction reaction?

Answer 27

A reaction in which hydrogen is added to or oxygen is removed from an organic compound.

Question 28

What is an oxidation reaction?

Answer 28

A reaction in which oxygen is added to or hydrogen is removed from an organic compound.

Question 29

Which compound undergoes Electrophilic addition reaction?

Answer 29

Alkenes undergo electrophilic addition reaction, alkenes undergo Hydration, Hydro halogenation or Halogenation.

Question 30

Which compound undergoes electrophilic substitution reaction?

Answer 30

Arenes or aromatic compounds undergo electrophilic substitution reaction. They undergo Halogenation, Nitration, alkylation and acylation which are electrophilic substitution reactions.

Question 31

Which compounds undergo nucleophilic addition reaction?

Answer 31

Carbonyl compounds undergoes nucleophilic substituition reaction. They react with HCN, NaOH, ethanol.