OCHEM EXAM ONE

methane

C H4

ethane

C2 H6

propane

C3 H8

butane

C4 H10

pentane

C5 H12

hexane

C6 H14

heptane

C7 H16

octane

C8 H18

nonane

C9 H20

decane

C10 H22

undecane

C11 H24

dodecane

C12 H26

eicosane

C20 H42

isopropyl

isobutyl

secbutyl

tertbutyl

neopentyl

principal quantum number

n = 1,2,3…

tells us how much ENERGY the orbital has (1s vs 2s)

describes how willing the electrons in that orbital are to leave

angular momentum quantum number

l = 0→(n-1)

tells us the SHAPE of the orbital (s=0, p=1, d=2)

magnetic quantum number

ml = -l → +l

tells us how many ORBITALS there are

• n² = ml

• 2l + 1 = ml

nodes

nodes are where e- density = 0

orbitals have n-1 nodes

planer node

2p orbital

spherical node

3p orbital (consists of spherical and planar node)

best lewis structure

formal charge = 0

if there has to be formal charges, lowest # is better

neg formal charge should be on most electroneg atom

resonance structures

hybrid (combo of equally valid structures) will have partial bonds and partial charge

bond order = total bonds / attached atoms

charge = charge on each atom / # of atoms

hybridization (VBT)

look @ molecule and count e- groups around the atom

• bonds (single, double or triple) count as one, lone pairs are one

sp³ = tetrahedral - 109.5

sp² = trigonal planar = 120

sp = linear = 180

ex) CH4 = sp³ (bc C has 4 bonds)

dihedral angle

angle btw atoms from rotating a plane

major resonance structures

• lone pair next to a pi bond

• pos charge next to a pi bond

• lone pair next to pos charge

• pi bond btw 2 atoms w diff electronegativity

molecular orbital theory (MO)

• if e- sin waves add constructively, e- density will incr btw the nuclei (bond!)

• if they add destructively, e- will decr btw the nucli (antibonding)

each bond (sigma or pi) has bonding and antibonding (*) orbitals

on energy level, antibonding is above bonding

checking if molecule exists with MO

if the bond order from MO (#e in bonding - #e in antibonding)/2

is the same as the bond shown in the lewis structure, then molecule exists

if BO from MO = 0 then molecule doesnt exist

paragmagnitism of O2

there are unpaired e- in the pi*2py orbital of O2, giving the paramagnietic (its affected by magnetic fields) properties to the molecule

frontier molecular orbital (FMO)

for rxn to occur, reactants have to overcome a significant energy barrier to get products

energy barriers exist bc of transition state - stablization of TS can allow rxn to happen, otherwise TS is very large

HOMO - highest occupied orbital

LUMO - lowest unoccupied orbital

after drawing MO, you can determine HOMO and LUMO → can see flow of e- bc HOMO goes into LUMO (can determine nucleophile and electrophile)

aliphatic hydrocarbons

alkanes, alkenes, alkynes

aromatic hydrocarbons

hydrocarbons in a benzene ring

formula for cycloalkanes vs unbranched alkane

cyclo: CnH2n

unbranched alkane: CnH2n+2

constitutional isomer

diff compounds with the same molecular formula

• differ in atom connectivity (structural isomers)

diff than resonance because single bonds are broken and no curved arrows can be drawn

conformational isomers

rotation around a single bond = conformers

staggered newman projection

staggered has a 60 degree dihedral angle

• if the two largest groups are 180 apart: anti

• if two largest groups are 60 apart: gauche

largest groups HAVE to be on diff carbons for there to be gauche/anti

eclipsed newman projection

dihedral angle is 0

always has TORSIONAL strain

less stable than staggered

steric strain

large functional groups close together

nomenclature tips

• same principle chain length = choose one with more substituents

• if chains the same - number the chain so that the first point of diff is smallest number

  • 3,3,5 trimethylpentane vs 5,5,3 trimethylpentane

  • if numbers still the same - lower number goes to first alphabetical group

• cyclo, neo iso = prefixes INCLUDED

• if noncylcic carbon chain has more Cs than the ring = treat it as a subsitituent

classification of carbons

primary carbon = bonded to 1 other carbon

secondary carbon = bonded to 2 other carbons

etc.

(classification of hydrogen depends on classification of the carbon it’s bonded to

ether (-oxy , - ane)

epoxide (-ene oxide)

aldehyde (-al)

ketone (-one)

carboxylic acid (-aic acid)

ester (-yl , -oate)

amide (-amide)

amine (-amine)

thiol

phenyl group

benzene ring acting as a substituent

can be represented by Ph-

alkyl groups

any alkane group as a substituent

can be represented by R

highly subsituted rings

use Ar-

aromatic ring acting as a substituent

(Ph is a specific type of Ar)

dotted vs solid lines

dotted = going AWAY

solid = coming TOWARDS

trend btw carbons and boiling pt

More carbons → higher boiling point because larger molecules have stronger London dispersion forces.

More branching → lower boiling point because branching decreases surface area/contact between molecules

melting pt

more symmetry = higher mp because the molecule can pack

even number of carbons = higher mp than odd number of carbons (when comparing adjacenty numbers)

lewis acid

accepts e- pair

lewis base

donates e- pair

nucleophile if it dontates e- pair to an atom thats NOT H

bronstead acid

proton donor

bronstead base

proton acceptor

always also a lewis base

curved arrows for lewis acid/base

gores from lewis base to lewis acid

strength of acid (pKa and Ka)

incr strength = DECR pka and INCR ka

equilibria in acid-base rxns

side with weaker acid and weaker base is favored

1) charge effect

pos charged compounds attract e- easier than neutral charged ones

pos charge makes compound more acidic

2) element effect

stronger acid = acidic proton is attached to an element thats more electroneg OR larger radius

3) hybridization effect

sp3 < sp2 < sp (incr acid strength)

sp is 50% s properties so therefore e-s are held closer to the nuecleus

want conj base to be more stable bc means smaller deltaG and therefore smaller pKa

4) resonance effect

resonance stabilization of conj base makes it more acidic

so if theres resonance structures - molecule is more acidic than one without any

5) polar effect

the more electronegative atoms = more partial pos charge to balance out a neg charge = stronger acid

• these are electron-withdrawing groups

closer the electroneg group is to the acidic proton = greater effect on its acidity

electron withdrawing group order of strength

O2N

(CH3)3N

N (triple bond) C

F

Cl

Br

I

CH3O

phenyl

electron donating substituents

carboxy

trimethyl siyl

ethyl