Revision: Basic Principles of Organic Chemistry Chemistry HSC Science (General) 11th Standard Maharashtra State Board

The branch of chemistry that deals with compounds originally derived from living organisms, such as sugar, starch, proteins, and acetic acid.

or

Organic compounds are the hydrides of carbon (hydrocarbons) and their derivatives. The branch of chemistry dealing with these compounds is called organic chemistry.

The branch of chemistry that deals with compounds obtained from non-living sources or minerals, such as common salt, blue vitriol, and nitrates.

Nomenclature is the system of assignment of names to organic compounds.

Compounds having the same molecular formula but different structural formula are known as Isomers and the phenomenon is known as Isomerism. (iso = same, meros = parts).

2D Representations

Type	Description	Example
Dash (Structural) Formula	Shows all atoms and all covalent bonds by dashes	\[\begin{array}{cc} \phantom{.....}\ce{H}\phantom{.....}\ce{H}\phantom{....}\ce{H}\phantom{.....}\\ \phantom{.....}|\phantom{.....}|\phantom{.....}|\phantom{......}\\ \phantom{.}\ce{H-C-C-C-H}\phantom{..}\\ \phantom{.....}|\phantom{.....}|\phantom{.....}|\phantom{......}\\ \phantom{.....}\ce{H}\phantom{....}\ce{H}\phantom{....}\ce{H}\phantom{.....} \end{array}\]
Condensed Formula	Groups atoms together without showing all bonds	CH₃CH₂CH₃ or CH₃–CH₂–CH₃
Bond Line / Zig-Zag Formula	Skeletal structure — lines represent C–C bonds; carbon atoms at line intersections and ends; H atoms implied

3D Representations

(i) Based on Functional Group:

(ii) Based on Carbon Skeleton:

• The IUPAC system provides a unique, systematic way to name carbon compounds based on structure, replacing confusing common names.
• An IUPAC name has three parts: prefix, parent, and suffix, reflecting the carbon chain and functional group.
• The parent name is based on the longest carbon chain, and its ending changes to –ane, –ene, or –yne depending on the number of bonds.
• Functional groups are shown as prefixes or suffixes, and the chain is numbered to give them the lowest possible number.
• If the suffix begins with a vowel, the final ‘e’ in the parent alkane name is dropped (e.g., propane → propanone).

1. Structural Isomerism

Same molecular formula but different connectivity (bonding) of atoms.

Types:

1. Chain isomerism: Different carbon skeleton (straight/branched)
2. Position isomerism: Functional group at different positions
3. Functional isomerism: Different functional groups (e.g., alcohol vs ether)
4. Metamerism: Different alkyl groups on either side of same functional group
5. Tautomerism: Dynamic equilibrium between two forms (keto ↔ enol)

2. Stereoisomerism

Same molecular formula and bonding but different spatial arrangement.

Types:

I. Geometrical isomerism:

• Due to restricted rotation (double bond)
• Forms cis (same side) and trans (opposite side)

II. Optical isomerism:

• Mirror image isomers (enantiomers)
• Show optical activity (rotate plane polarized light)