Chapter 1: Structure and Bonding

Lewis Structures and Valence Electrons

• Lewis structures represent the arrangement of valence electrons among atoms in a molecule.

• To draw a complete Lewis structure:

  1. Count the total number of valence electrons for all atoms.

  2. Arrange atoms with the least electronegative atom in the center (except hydrogen).

  3. Connect atoms with single bonds, then distribute remaining electrons to satisfy the octet rule.

• Formal charge is calculated as:

Resonance Structures

• Resonance structures are different Lewis structures for the same molecule, showing delocalization of electrons.

• Rules for resonance:

  • Only electrons move, not atoms.

  • Major contributors have the lowest formal charges and full octets on electronegative atoms.

Condensed and Line-Angle Structures

• Condensed structures omit some or all bonds, grouping atoms together (e.g., CH3CH2OH).

• Line-angle structures use lines for bonds and vertices for carbons; hydrogens on carbons are implied.

Hybridization and Molecular Shapes

• Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals.

• Key types:

  • sp: linear geometry, 180° bond angle

  • sp2: trigonal planar, 120° bond angle

  • sp3: tetrahedral, 109.5° bond angle

• Identify hybridization by counting regions of electron density around the atom.

Orbital Diagrams

• Show the arrangement of electrons in atomic or molecular orbitals.

• Double bonds involve one sigma (σ) and one pi (π) bond; triple bonds have one σ and two π bonds.

• Label diagrams with bond angles and hybridization for clarity.

Chapter 2: Acids, Bases, and Functional Groups

Electronegativity and Dipoles

• Electronegativity differences create bond dipoles (arrow points toward more electronegative atom).

• Nonbonded electron pairs also create dipoles; overall molecular dipole is the vector sum of all bond and lone pair dipoles.

Acid-Base Theories

• Brønsted-Lowry acid: proton (H+) donor; base: proton acceptor.

• Lewis acid: electron pair acceptor; Lewis base: electron pair donor.

• Nucleophile: electron-rich species (Lewis base); Electrophile: electron-poor species (Lewis acid).

Acid-Base Equations and Conjugate Pairs

• Acid-base reactions can be represented as:

• Use curved arrows to show electron flow from base to acid.

• Direction of reaction is predicted using pKa values: reaction favors formation of the weaker acid/base (higher pKa).

Functional Groups

• Recognize and name common functional groups (e.g., alcohols, ethers, amines, carboxylic acids, etc.).

Chapter 3: Structure and Stereochemistry of Alkanes

Nomenclature of Alkanes and Cycloalkanes

• Follow IUPAC rules: identify the longest carbon chain, number to give substituents lowest numbers, name and order substituents alphabetically.

• Complex substituents are named as branched alkyl groups.

Newman Projections and Conformations

• Newman projections visualize conformations by looking down a C–C bond.

• Staggered conformation: lowest energy; eclipsed: highest energy.

Ring Strain in Cycloalkanes

• Sources of strain:

  • Angle strain: deviation from ideal bond angles

  • Torsional strain: eclipsing interactions

  • Steric strain: crowding of bulky groups

• Cyclopropane and cyclobutane have significant angle and torsional strain; cyclopentane and cyclohexane are more stable.

Cyclohexane Conformations

• Chair conformation is most stable; boat and twist-boat are higher in energy.

• Potential energy diagram shows relative energies:

• Cis/trans isomerism in disubstituted cyclohexanes affects stability; equatorial substituents are favored.

Chapter 4: The Study of Chemical Reactions

Free-Radical Mechanisms

• Consist of three steps:

  1. Initiation: generates radicals

  2. Propagation: radicals react to form new radicals

  3. Termination: radicals combine to end the chain

• Example: Halogenation of alkanes

Thermodynamics of Reactions

• Calculate enthalpy change () for each step:

• Propagation steps can be exothermic or endothermic.

Hammond Postulate and Energy Diagrams

• The Hammond Postulate relates the structure of the transition state to the energies of reactants and products.

• Potential energy diagrams illustrate the energy changes during a reaction.

Classification of Hydrogens and Reactive Intermediates

• Hydrogens are classified as primary, secondary, or tertiary based on the carbon they are attached to.

• Stability trends:

  • Carbocations: tertiary > secondary > primary

  • Free radicals: tertiary > secondary > primary

  • Carbanions: primary > secondary > tertiary

  • Carbenes: neutral, divalent carbon species

Chapter 5: Stereochemistry

Isomerism

• Constitutional isomers: same formula, different connectivity.

• Stereoisomers: same connectivity, different spatial arrangement.

Chirality and Enantiomers

• Chiral molecules are non-superimposable on their mirror images; achiral are superimposable.

• Enantiomers are a pair of chiral molecules that are mirror images.

Assigning Configuration: (R) and (S)

• Assign priorities to substituents using the Cahn-Ingold-Prelog rules.

• Orient the lowest priority group away; trace from highest to lowest priority:

  • Clockwise: (R)

  • Counterclockwise: (S)

Optical Activity and Racemic Mixtures

• Specific rotation () is measured using: where is observed rotation, is path length (dm), is concentration (g/mL).

• Racemic mixture: 1:1 mixture of enantiomers; optically inactive.

Fischer Projections and Stereoisomer Counting

• Fischer projections are 2D representations of 3D molecules; rules govern rotation and conversion to perspective drawings.

• Number of stereoisomers: , where is the number of chiral centers.

• Meso compounds: achiral despite chiral centers due to internal symmetry.

Physical Properties of Stereoisomers

• Enantiomers have identical physical properties except for optical rotation.

• Diastereomers differ in all physical properties.

Chapter 6: Alkyl Halides and Nucleophilic Substitution

Nomenclature of Alkyl Halides

• Name halogen substituents as prefixes (e.g., bromo-, chloro-), include (R)/(S) if chiral centers are present.

Allylic Bromination

• Selective bromination at the allylic position (next to a double bond) via a radical mechanism.

SN2 Reaction Mechanism

• One-step, concerted mechanism; nucleophile attacks as leaving group departs.

• Inversion of configuration at the reaction center.

• Favored by primary substrates, strong nucleophiles, and polar aprotic solvents.

SN1 Reaction Mechanism

• Two-step mechanism: formation of carbocation intermediate, then nucleophilic attack.

• Racemization occurs due to planar intermediate.

• Favored by tertiary substrates, weak nucleophiles, and polar protic solvents.

SN1 vs. SN2 Comparison

Chapter 7: Structure and Synthesis of Alkenes; Elimination

Elements of Unsaturation (Index of Hydrogen Deficiency, IHD)

• IHD indicates the number of rings and/or multiple bonds in a molecule.

• Formula: where C = carbons, N = nitrogens, H = hydrogens, X = halogens.

Nomenclature of Alkenes (E/Z)

• Number the chain to give the double bond the lowest number.

• E/Z designation:

  • E (entgegen): higher priority groups on opposite sides

  • Z (zusammen): higher priority groups on same side

E1 and E2 Elimination Mechanisms

• E1: two-step, forms carbocation intermediate; possible rearrangements.

• E2: one-step, concerted; requires anti-coplanar geometry.

• Zaitsev’s rule: major product is the more substituted alkene.

Alcohol Dehydration

• Alcohols can be dehydrated to form alkenes via E1 (acid-catalyzed) or E2 (with strong base) mechanisms.

E1 vs. E2 Comparison

Chapters 8 & 9: Reactions of Alkenes and Alkynes

Nomenclature

• Name alkenes and alkynes by identifying the longest chain containing the multiple bond and numbering to give the bond the lowest number.

Reactions of Alkenes

• Identify substrate (alkene), reagents, and products for major reaction types (e.g., addition of HX, hydration, halogenation, hydroboration-oxidation).

Reactions of Alkynes

• Focus on major reactions: addition of HX, hydration, reduction, and oxidative cleavage.

• Identify substrate, reagents, and products for each reaction.