Final exam

bond order equation

(# of e’s in bonding MOs - # of e’s in antibonding MO)/2

linear

• AX2E0

• no LP

• sp hybridized

• 180 degrees

• ex: CO₂

bent

• AX2E1 or AX2E2

• 1 or 2 lone pairs around central atom

• sp2 hybridized

• 1 LP ex: SO2

• 2 LP ex: H2O

trigonal planar

• AX3E0 or AX3E1

• 0 LP

• 1 LP

  • electron geometry is trigonal planar

  • molecular geometry is bent

• sp2 hybridized

• 120 degrees

• 0 LP ex: BF3

• 1 LP ex: SO2

trigonal pyramidal

• AX3E1

• 1 lone pair

• sp3 hybridized

• ex: NH3 or H3O

tetrahedral

• AX4E0

• zero lone pairs

• sp3 hybridized

• 109.5 degrees

• example: NH4+, CH4

resonance structure pneumonic

• Octet: contributor with full octet of all atoms is MOST important

• En: the more Electronegative gets the electrons and negative formal charge. Use only if rule 1 can’t be satisfied

• Cs: minimize Charge and minimal Separation of opposite charges

  • opposite charges should be as close together as possible because it lowers the systems energy, making the resonance structure more stable

constitutional isomers

• different compounds with the same molecular formula but a different connectivity

• both are C4H10

isopropyl (i-Pr)

(CH3)2CH

isobutyl (i-Bu)

(CH3)2CHCH2

sec-butyl (s-Bu)

tert-butyl (t-bu)

(CH3)3C

neopentyl

(CH3)3CCH2

cyclopropane

cyclobutane

cyclopentane

cyclohexane

primary carbon

carbon bonded to one carbon atom

secondary carbon

carbon bonded to two other carbon atoms

tertiary carbon

carbon bonded to three other carbon atoms

quaternary carbon

carbon bonded to four other carbon atoms

primary hydrogen

hydrogen bonded to a primary carbon

secondary hydrogen

hydrogen bonded to a secondary carbon

tertiary hydrogen

hydrogen bonded to a tertiary carbon

primary alcohol

the carbon attached to the alcohol is attached to one other carbons

secondary alcohol

the carbon attached to the alcohol is attached to two other carbons

tertiary alcohol

the carbon attached to the alcohol is attached to three other carbons

primary amine

the carbon attached to the amine is attached to one other carbons

secondary amine

the carbon attached to the amine is attached to two other carbons

tertiary amine

the carbon attached to the amine is attached to three other carbons

primary halide

the carbon attached to the halide is attached to one other carbons

secondary halide

the carbon attached to the amine is attached to two other carbons

tertiary halide

the carbon attached to the amine is attached to three other carbons

torsional straing

arises when nonbonded atoms separate by three bonds are forced from a staggered conformation to an eclipsed

hyperconjugation

stabilization arises from a small donor-acceptor interaction between a filled C-H bonding MO of one carbon and the empty or unfilled C-H antibonding MO on an adjacent carbon

dihedral angle

angle created by two intersecting planes on Newman projection

strain

• measure of the energy stored in a compound due to structural distortion

• type: torsional strain, steric strain, and angle strain

bronsted acids

• proton donors

  • lose an H

• e sink: donating H+ without electron

  • arrow head

bronsted bases

• proton acceptors

  • gain an H

• e sources: negative charge or lone pair

  • arrow tail

lewis acids

• accept electrons

• e sink

  • arrow head

lewis bases

• donate electrons

• e source: lone pairs and negative charge

  • arrow tail

nucleophiles

• lewis bases

• electron rich (-)

• use their electrons to ATTACK the nucleus

  • arrow tail

electrophiles

• lewis acids

• electron poor (+)

  • arrow head

factors the affect acid/base strength

• charge

  • lack of electrons increases acidity (plus charge)

• Atom size/ polarizability

  • greater atom size means greater electron delocalization and increased acidity

  • trumps electronegativity

• electronegativity

  • hydrogens on electronegative atoms are more acidic and easier lose since the more electronegative atom has greater affinity for electrons

  • think: how greedy is this atom for electrons?

• inductive effect

  • electronegative atoms increase acidity by pulling electron density away through a sigma bond.

  • This stabilizes the negative charge on the conjugate bases.

  • The closer the electronegative atom is to the acidic H, the stronger the effect

  • think: how does an electronegative atom affect the rest of the molecule?

• resonance stabilization

  • conjugate base will be stabilized with greater electron delocalization due to resonance

  • the more contributors the conjugate base has, the more acidic it is

• orbital hybridization

  • due to high s character in the hybrid orbital bonded to the acidic hydrogen increases acidity because the electrons in the conjugate base are held closer to the nucleus making it more stable

stability of alkenes

• more alkyl group substitution around the pi-bond the more stable the alkene

• trans is MORE stable than cis meaning lower (less exothermic) hydrogenation

• reason: hyper-conjugation: sigma bonding electrons can delocalize or enter pi-star orbitals

• reaction rate for ELIMINATIONS is tertiary substrate>secondary>primary

  • because greater substitution generates a more stable alkene

Markovnikov’s rules

hydrogen adds to the carbon with the more hydrogens

anti addition via bridged intermediates

• electrophile and nucleophile add from opposite sides

  • addition of halogens (Cl2, Br2 additions)

  • oxymercuration/reduction (Markovnikov addition): hydration of pi bond

syn addition

• electrophile and nucleophile add from the same face/side

  • hydroboation/oxidation (anti-Markovnikov addition): hydration of pi bond

regioselectivity

• whee does H go?

• anti-markovnikov addition

stereospecificity

• syn addition

  • add from the same face - H and OH end up cis to each other)