Organic Chemistry Formulae & Basic Concepts

Question-and-Answer flashcards covering definitions, examples, and key comparisons for types of chemical formulae, homologous series, functional groups, and isomerism in organic chemistry.

What are the five main types of formula used in organic chemistry?

Empirical, Molecular, General, Structural, and Displayed formulae (a sixth common one is the Skeletal formula).

What does an empirical formula show?

The simplest whole-number ratio of atoms of each element in a compound.

What is the empirical formula of C₂H₆?

CH₃

What does a molecular formula show?

The actual number of atoms of each element present in one molecule of a compound.

What is the molecular formula of butane?

C₄H₁₀

What is a general formula in organic chemistry?

An algebraic expression that represents the composition of every member of a homologous series.

What is the general formula for alkanes?

CₙH₂ₙ₊₂

What is the general formula for alkenes?

CₙH₂ₙ

What is the general formula for alcohols?

CₙH₂ₙ₊₁OH

What does a structural formula show?

The arrangement of atoms in a molecule without displaying every bond.

What does a displayed formula show?

All the atoms and every bond present in a molecule.

What does a skeletal formula show?

Only the carbon backbone (as zig-zag lines) and functional groups, omitting C–H bonds.

What is a homologous series?

A family of organic compounds with the same functional group, the same general formula, similar chemical properties, a gradual change in physical properties, and successive members differing by a CH₂ unit.

What is a functional group?

A specific group of atoms responsible for the characteristic chemical reactions of a molecule, e.g., C=C in alkenes, –OH in alcohols, –COOH in carboxylic acids.

What are isomers?

Molecules that have the same molecular formula but different structures; includes structural isomerism (different bonding patterns) and stereoisomerism (same bonds, different spatial arrangement).

How does an empirical formula differ from a molecular formula?

Empirical formula gives the simplest whole-number ratio of atoms, while the molecular formula gives the actual number of each type of atom in the molecule (e.g., CH₃ vs. C₂H₆ for ethane).