chapter 4: drawing organic molecules & IHD & isomerism

What conventions are used in line-bond structures?

Ends/vertices = carbon atoms

Lines = bonds

Hydrogens on carbon are implicit

Heteroatoms must be shown explicitly

What defines saturation?

A saturated molecule has the maximum number of hydrogens (CnH₂n+2 for hydrocarbons). Fewer hydrogens means unsaturation due to rings or π bonds. This is the foundation of IHD.

What does Index of Hydrogen Deficiency (IHD) represent?

IHD equals the number of rings and/or π bonds in a molecule. Each degree corresponds to one ring or one π bond.

IHD = 2(# of carbons) + 2 - (# of hydrogens)/2

Example:

C4H10

IHD = 2(4)+2-10/2 = 0

0 rings or 0 π bonds.

How do heteroatoms affect IHD?

Halogens = treat as H

Oxygen = ignore

Nitrogen = add one H equivalent

Formula w/ nitrogen = (2n+2-H+N)

n = # of carbons

H = # of hydrogens

N = # of nitrogens

What are isomers?

Molecules with the same molecular formula but different structures with different atom-to-atom connections.