Study Guide: Organic Chemistry Fundamentals (Chapters 3/4)

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Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.

Definition: A functional group is an atom or group of atoms that imparts certain chemical properties to a molecule.
Identification: Be able to look at a molecular structure and identify the functional groups present (e.g., alcohol, ketone, carboxylic acid, amine).
Application: Translate a list of functional groups into a skeletal structure.
Example: The hydroxyl group (-OH) is the functional group of alcohols.

Isomers are compounds with the same molecular formula but different structures or spatial arrangements.

Types: Structural isomers (different connectivity) and stereoisomers (same connectivity, different spatial arrangement).
Identification: Be able to draw or identify isomers from a given molecular formula or structure.
Example: C4H10 can be butane (straight chain) or isobutane (branched).

Alkyl groups are substituents derived from alkanes by removing one hydrogen atom.

Common Abbreviations: Me (methyl, -CH3), Et (ethyl, -C2H5), Pr (propyl), Bu (butyl).
Application: Know how to interpret and use these abbreviations in molecular structures.

Nomenclature is the system of naming chemical compounds.

Alkanes: Saturated hydrocarbons with the general formula CnH2n+2.
Cycloalkanes: Saturated hydrocarbons with a ring structure, general formula CnH2n.
Naming: Name the structure and vice versa (convert name to structure).
Example: Cyclohexane is a six-membered ring with formula C6H12.

Carbons and hydrogens in organic molecules are classified based on their connectivity.

Primary (1°): Carbon attached to one other carbon.
Secondary (2°): Carbon attached to two other carbons.
Tertiary (3°): Carbon attached to three other carbons.
Quaternary (4°): Carbon attached to four other carbons.
Application: Be able to identify and classify carbons/hydrogens in a given structure.

Hydrocarbons are compounds composed only of carbon and hydrogen.

Intermolecular forces are forces of attraction or repulsion between molecules.

Types: London dispersion forces, dipole-dipole interactions, hydrogen bonding.
Application: Use these forces to rank alkanes in order of increasing/decreasing boiling/melting points.
Example: Larger alkanes have higher boiling points due to increased London dispersion forces.

Solubility is the ability of a substance to dissolve in a solvent, often influenced by polarity.

Polarity: Polar molecules dissolve in polar solvents; nonpolar molecules dissolve in nonpolar solvents ("like dissolves like").
Application: Use intermolecular forces to predict solubility in a given solvent.

Newman projections are a way to visualize the conformation of a molecule by looking straight down a carbon-carbon bond.

Conformations: Staggered (more stable), eclipsed (less stable), gauche (a type of staggered with groups 60° apart).
Application: Draw and interpret Newman projections, comment on stability.
Example: In ethane, the staggered conformation is more stable than the eclipsed conformation.

Strain in molecules arises from deviations from ideal bond angles or from atoms being forced too close together.

Torsional Strain: Resistance to twisting about a bond, as in eclipsed conformations.
Angle Strain: Deviation from ideal bond angles (109.5° for sp3 carbons).
Steric Strain: Repulsion between atoms or groups that are too close together.
Application: Use Newman projections and strain values to calculate and compare stability.
Example: Cyclopropane has significant angle strain due to its 60° bond angles.

Ring strain is the extra energy present in a cyclic molecule due to angle, torsional, and steric strain.

1,3-Diaxial Interactions: Steric interactions between axial substituents on cyclohexane rings separated by one carbon.
Application: Calculate 1,3-diaxial strain in cyclohexane derivatives.

In cyclohexane, substituents can occupy axial (parallel to the ring axis) or equatorial (around the equator of the ring) positions.

Stability: Bulky groups prefer the equatorial position to minimize 1,3-diaxial interactions.
Application: Identify axial/equatorial positions and predict the most stable conformation.

Cyclohexane can adopt several conformations, with the chair being the most stable due to minimized strain.

Chair Conformation: All bond angles are close to 109.5°, minimizing strain.
Boat Conformation: Less stable due to steric and torsional strain.
Application: Distinguish between chair and boat conformations and understand their relative stabilities.

Type of Strain	Description	Example
Torsional Strain	Repulsion from eclipsed bonds	Ethane in eclipsed conformation
Angle Strain	Deviation from ideal bond angles	Cyclopropane (60° angles)
Steric Strain	Atoms/groups forced too close together	1,3-diaxial interactions in cyclohexane