Organic Molecules: Chains, Isomers, and Macromolecules

Organic compounds are based on carbon and hydrogen; carbon is tetravalent, enabling diverse structures.
Fossil fuels are hydrocarbons; hydrocarbons form the backbone of many everyday molecules.

Chains can be unbranched or branched; each carbon forms four bonds to C or H.
Double bonds change connectivity; rings are another common representation, with carbons at joining points and hydrogens filling remaining valences.
The same molecule can be drawn as a chain or a ring.
Example formulas to recall: $C8H{18}$ and $C{20}H{42}$ .

Isomers have the same formula but different structures.
Structural isomers: different covalent arrangements; more carbons/hydrogens lead to more possible isomers (e.g., many for $C8H{18}$ ).
Geometric (cis/trans) isomers: same covalent arrangement around a double bond; cis = same side, trans = opposite sides.
Enantiomers (chirality): non-superimposable mirror images around an asymmetric carbon; L and D forms; biology often prefers one form (e.g., amino acids L, sugars typically D).

Functional groups are reactive moieties that drive chemistry.
Common groups include hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2), phosphate (-PO4H_2); others exist.
These groups influence reactivity and hydrophilicity.

Macromolecules are polymers made of repeating monomers.
Examples: proteins (amino acids), nucleic acids (nucleotides), carbohydrates (simple sugars).
Condensation (dehydration) reactions build polymers with the release of water (H from one monomer, OH from another).
Hydrolysis is the reverse: water is added to break polymers into monomers; enzymes assist digestion.

The sequence of monomers determines structure and function (e.g., amino acids in proteins; nucleotides in RNA).
Polymers can be drawn as chains or rings; carbons are numbered along chains to indicate structure.