Introduction to Functional Groups:

 Title: Introduction to Functional Groups:

In organic chemistry, functional groups are specific groups of atoms within a molecule that determine the molecule's chemical behaviour and properties. They are responsible for the characteristic chemical reactions of organic compounds. For example, alcohol molecules contain a hydroxyl (-OH) functional group, while carboxylic acids contain a carboxyl (-COOH) functional group. These functional groups can help us predict how the molecule will react in various chemical conditions.

Hydrocarbons are organic compounds that are made entirely of carbon (C) and hydrogen (H) atoms. They are divided into four classes: alkanes, alkenes, alkynes, and aromatic hydrocarbons. Alkanes, in particular, are saturated hydrocarbons, meaning all their carbon-carbon bonds are single bonds.

Alkanes – Structure, Sources, and Physical Properties:

Alkanes have the general formula CnH2n+2, where n represents the number of carbon atoms in the molecule. They are characterized by the presence of only single bonds between carbon atoms. For example, methane (CH4), ethane (C2H6), and propane (C3H8) are all alkanes.

Sources:

1. Natural gas: Methane, ethane, and propane are major components of natural gas, which can be found in fossil fuel deposits.

2. Petroleum: Alkanes can be obtained from the fractional distillation of crude oil.

3. Biological sources: Some alkanes can be produced by certain plants and microorganisms.

Physical Properties:

1. Nonpolar nature: Alkanes are nonpolar compounds due to the presence of only C–H and C–C bonds. They are hydrophobic and insoluble in water but soluble in nonpolar solvents (e.g., hexane dissolves in benzene).

2. Boiling and melting points: These increase as the size of the alkane increases. The reason is that larger molecules have more dispersion forces which require more energy to overcome.

3. Flammability: Alkanes are highly flammable, and their combustion results in water and carbon dioxide.

IUPAC Naming, Cycloalkanes, and Bicyclo Compounds:

IUPAC (International Union of Pure and Applied Chemistry) has set rules for naming organic compounds to avoid ambiguity. For alkanes, the steps are as follows:

1. Identify the longest carbon chain and name using the appropriate alkane suffix (e.g., -ane).

2. Number the carbons in the chain, starting from the end closest to any substituents (branch groups).

3. Name and number the substituents.

4. Write the complete name with the substituents in alphabetical order, followed by the parent alkane name, with their positions denoted by the numbers determined in Step 2.

Example: For the molecule CH3CH(CH3)CH2CH3, the parent chain is butane (4 carbons). The methyl group is at position 2. The IUPAC name is 2-methyl butane.

Cycloalkanes are alkanes that form a closed ring structure. Their general formula is CnH2n. An example is cyclohexane (C6H12). Bicyclo compounds are compounds with two fused rings that share two or more carbon atoms. An example is bicyclo[2.2.1]heptane.

Isomerism:

Isomerism occurs when two or more compounds have the same molecular formula yet distinct structural arrangements. In alkanes, there are two types of isomerism:

1. Structural (constitutional) isomerism: Isomers have the same molecular formula but distinct connections between atoms. For example, butane (C4H10) can be arranged as a continuous chain (n-butane) or with a branch (2-methylpropane).

2. Stereoisomerism (specifically in cycloalkanes): Stereoisomers have the same connectivity of atoms but differ in their 3D arrangement in space. The most common form is cis-trans isomerism, occurring in cycloalkanes with substituents on the ring. For example, cis-1,2-dimethyl cyclopentane has the methyl groups on the same side of the ring, while trans-1,2-dimethyl cyclopentane has them on opposite sides.