LSU CHEM 2261 Exam 1 - Davila Fall 2026

Formal Charge

Valence e - (nonbonding e + (1/2)(bonding e))

Constitutional Isomers

Same Molecular formula, different connectivities

Delocalized Electrons

electrons that are shared by more than 2 atoms

Resonance energy

extra stability a compound gains for having delocalized electron

sigma bond

bond formed by head to head overlap of atomic orbitals; of any bond the first is a sigma, rest are pi

pi bond

bond formed by side to side overlap of p-atomic orbitals

antibonding molecular orbitals

contain a node between the nuclei

VSEPR model

pairs of valence electrons around an atom repel each other

sp3 hybridization

atom can only form single bonds

sp2 hybridization

molecules containing a double bond

sp hybridization

molecules containing an atom with triple or double bonds

acid

donates a proton

base

accepts a proton

conjugate acid

the base after it accepts the proton

conjugate base

the acid after it gives away the proton

Acid dissociation constant (Ka)

measures the strength of an acid

Induction

shifting of electrons in a bond as a result of the electronegativity of nearby atoms.

Lewis Acid (electrophile)

a substance that accepts 2 electrons.

Lewis Base (nucleophile)

a substance that donates 2 electrons.

Alkanes:

hydrocarbons that contain only C-C and C-H single bonds. Molecular formula: Cn H2n+2

Constitutional isomers:

The number of isomers increases dramatically as the number of carbon atoms increases.

Cycloalkanes:

CnH2n

Alkenes:

Unsaturated hydrocarbons that contain a C=C bond with Molecular formula: CnH2n

Cis-Trans Isomers:

Compounds that have the same molecular formula, same connectivities but different arrangement in space.Alkynes:

Alkynes:

Unsaturated hydrocarbons that contain a C≡C bond with Molecular formula: Cn H2n-2

Aromatic Compounds:

Hydrocarbons related to benzene

Alkyl (R) groups:

obtained by removing a hydrogen atom from an alkane.

primary carbon

bonded to one other carbon, a primary hydrogen is bonded to a primary carbon.

secondary carbon(2 degree , sec-)

bonded to two other carbons, a secondary hydrogen is bonded to a 2o carbon.

tertiary carbon (3o , tert-)

bonded to three other carbons, a tertiary hydrogen is bonded to a 3o carbon

quaternary carbon

bonded to four other carbons.

alcohol

replacement of H of an alkane by OH, NH2 or a halogen (F, Cl, Br, or I)

Functional group

an atom or group of atoms where most of the chemical reactions occur. They usually contain multiple bonds or lone pairs of electrons.

Functional group that contains C-C multiple bonds:

functional group that contain carbon bonded to an electronegative atom:

functional group that contain a carbonyl group (C=O):

Melting point trends

Boiling point trends

Cycloalkanes

CnH2n

Newman projections

viewing the molecule along the C-C bond, so the back C is hidden by the front C.

Torsional strain

repulsion between the bonding electrons of one substituent as they pass close to the bonding electrons of another substituent.

Steric strain

results when atoms or groups are too close to each other.

anti conformation

the largest substituents are opposite each other , most stable conformation

gauche conformations

the largest substituents are adjacent to each other

Angle Strain

(deviation from 109.5° bond angle)

Torsional Strain

(repulsion of the bonding electrons between nearby substituents)

Steric Strain

(caused by atoms or groups of atoms approaching each other too closely)

CHAIR and BOAT

Conformations in Cyclohexane, Both conformations are free of angle strain; however, the boat conformer has more torsional and steric strain than the chair.

Ring-flip:

cyclohexane interconverts between two chair conformations (interconversion of axial and equatorial positions):Substituents in axial positions

Substituents in axial positions

1,3-diaxial interactions (unfavorable steric interactions).

Substituents in equatorial positions

have fewer steric interactions (favorable).

Stereoisomers

have different spatial orientation

Cis-trans stereoisomerism

(cis = same side, trans = opposite side)