Organic Chemistry Exam Notes: Key Concepts and Practice

Molecular Formula Example: The hormone being discussed has the molecular formula C{19}H{25}NO.
Hybridization (sp^3):
- Occurs when a central atom has four connections (regions of electron density).
- Examples include carbons with four single bonds (e.g., CH_4) or a carbon directly bonded to four other atoms/groups.
- For nitrogen, if it has three single bonds and one lone pair, it is also sp^3. The presence of an H (hydrogen) often signifies an sp^3 carbon if it results in four total connections.
Hybridization (sp^2):
- Occurs when a central atom has three connections.
- A double bond counts as one connection for hybridization purposes. Therefore, a carbon with a double bond and two single bonds would be sp^2.
- The example shown has a carbon with a double bond and two other connections, totaling three connections.
Hybridization (sp):
- Occurs when a central atom has two connections.
- This typically involves a triple bond (e.g., alkyne carbon) or two double bonds (e.g., central carbon in allene).
- When considering a bond that connects a triple bond and a double bond (e.g., bond 'd' in a practice problem), one might describe the connection as sp^2-sp, considering the lowest bond order first for each side, or specifically indicating the hybridization of each atom in the bond.
- For Ochem 1, the questions on orbital overlapping are generally straightforward; Ochem 2 may introduce more complex orbital types.

109.5^ ext{o} Bond Angle: This angle is characteristic of atoms with four single bonds around a central atom (tetrahedral electron geometry).
- This applies when there are no double or triple bonds present.
- Example: A molecule with all single bonds exhibits bond angles of approximately 109.5^ ext{o}.
180^ ext{o} Bond Angle: This angle is characteristic of atoms involved in a triple bond (linear geometry).
Angles Less Than 109.5^ ext{o} ( ext{e.g., } 107^ ext{o}):
- Occur when a central atom has lone pairs of electrons, which exert greater repulsion than bonding pairs, compressing the bond angles.
- Example: Water (H2O) has a bent geometry with bond angles around 104.5^ ext{o} due to two lone pairs on oxygen. Ammonia (NH3) has a trigonal pyramidal geometry with bond angles around 107^ ext{o} due to one lone pair on nitrogen.
- The professor might sometimes approximate angles with lone pairs as 109.5^ ext{o} on exams, but technically they should be smaller.

Hexane Isomers: When drawing isomers of hexane (C6H{14}), you must ensure you have six carbons in total and do not form cyclic structures unless specified.
- You cannot