Organic Chemistry ADS lectures

Methyl

1 carbon, CH3, Me

Ethyl

2 carbon, CH2CH3, Et

Propyl

3 carbon, CH2CH2CH3, Pr

Butyl

4 carbon, CH2CH2CH2CH3

Phenyl group

Benzene ring attached to a molecule by only one of its atoms (Ph) ex. phenol, phenylalanine

isomers

non-identical molecules with the same molecular formula

branched carbon chaine types

n-normal/linear

i-iso

s-sec (secondary carbon)

t-tert (tertiary carbon, carbon attached to 3 other carbons)

Functional groups

the reactive sites of molecules

Alkenes

contain C-C double bonds, planar

Alkynes

Contain C-C triple bonds, linear

Alcohols

Contain a hydroxyl group (R—OH)

sp3 hybridized, tetrahedral

Ethers (R1—O1—R2)

Contain an alkoxy group n— 2 alkyl groups linked through a single oxygen atom; tetrahedral sp3 hybridized

Alkyl halides

Contain a bond to a halogen (R—X)

Amines

contain the amino group NH2 (R-NH2); tetrahedral sp3 hybridized

Nitro compounds

contain the nitro group (R—NO2); strong electron withdrawing group

Aldehydes

Contain carbonyl group (C=O) R—CHO

Ketones

Contain carbonyl group (C=O) R₁COR₂

Carboxylic Acids

contain carbonyl group CO₂H (R—CO₂H)

Esters

Contain a carboxyl group with an additional alkyl group R—CO₂—R

Nitriles or Cyanides

Contain the cyano group (C=N)

Naming Organic Compounds

Prefix (Name and position of substituent), Parent (length of the longest carbon chain), suffix (main functional group)

hybridization

Allows the mixing of atomic orbitals on the same atom to create hybrid atomic orbitals that point directly to the atoms we wish to construct bonds with

sp3 hybridized

When an atom is bonded to 4 other atoms

sp2 hybridized

when an atom is bonded to 3 other atoms

sp hybridized

when an atom is bonded to 2 other atoms

which orbitals do lone pairs go into? why?

low energy hybridized orbitals (sp^x) because they have some s character and s orbitals are held closer to the nucleus therefore it is more energetically favorable/stable to place lone pairs in them rather than a p orbital

where do empty/vacant orbitals go

atomic orbitals — not hybridized (p)

is rotation around a C=C bond possible?

No it is not possible because it requres breaking the pi bond

conformations

individual shapes of a molecule created through bond rotation —- no bonds broken when interconverting conformations

eclipsed conformation

H atoms on adjacent carbons are as close as possible

staggered conformation

H atoms on adjacent carbons are as far apart as possible

is staggered or eclipsed conformation more stable

staggered because it minimized torsional styrain from the electron-electron repulsions in adjacent C-H bonds

Steric strain

The interactions of substituents on adjacent carbon atoms

antiperiplanar

substituents on adjacent carbons are as far apart as possible (180º) — most stable conformation — staggered

Gauche/Synclinal

Next most stable conformation— staggered but still steric strain from substituents

ring/angle strain

the strain imparted onto bonds resulting from the deviation of the ideal 109.5º (tetrahedral)

most stable conformation of cyclohexane + why?

chair conformation - Staggered C-H interactions and gauche C—C interactions

Minimizes angle, torsional, and steric strain

equatorial bonds

Parallel to the C-C bonds in the ring

Axial bonds

alternating arrangement of bonds pointing up and down

Why is chair conformation more stable than boat?

C-H bonds are eclipsed, flagpole interactions (close proximity of H’s) — boat conformation has both steric and torsional strain

Ring-flip /ring inversion

The interconversion of axial and equatorial substituents (all axial H become equatorial and all equatorial H become axial) via bond rotation

Monosubstitued cyclohexanes

cyclohexanes with a substituent attached to the skeleton in either an axial or equatorial conformation

Which conformation of a monosubstituted cyclohexane is more stable? why?

In almost every case the conformer with the substituent equatorial is lower in energy (more stable) because the axial conformer has 1,3 diaxial interactions causing steric strain.

Also when the substituent is equatorial it is antiperiplanar to the C—C bonds in the ring which minimizes steric interactions — When axial it is gauche to C—C bonds which is less stable

Where does the equilibrium lie for axial vs equatorial isomers?

Lies to the right — equatorial position

How much equatorial isomer is present at equilibrium (depending on substituent)

As size of substituent chain increases K increases and the % of molecules with substituent equatorial approaches 100

Isomers

non-identical molecules with the same molecular formula

Constitutional isomers

isomers with different connectivity between atoms (sequences of bonds)

stereoisomers

isomers with the same atom connectivity that differ in spatial arrangement of atoms

cannot be interconverted by bond rotation

Achiral molecules

molecules that are superimposable upon their mirror image and contain a plane or center of symmetry

Chiral molecules

molecules that are non-superimposable upon their mirror image — usually contain stereogenic centers

enantiomers

structures that are non-superimposable mirror images of each other that have the same bond connectivity, identical physical properties, and different interactions with other chiral molecules

stereogenic center

general — an sp3 hybridized carbon atom with four different groups

center of symmetry

if a straight line is drawn from any part of an object throught its center and it arrives at an identical point an equal distance from the other side it is a point of symmetry

racemic mixture

a 50:50 mixture of enantiomers

enantiomerically pure

molecules that exist as single enantiomers

optical activity

Phenomenon where enantiomers rotated the plane of polarized light in equal but opposite directions — observed with polarimetry

Cahn-Ingold-Prelog rules (what do they do+ what are they)

Used to assign absolute conformation (R) or (S) to a or a stereogenic element

Assign priority (highest atomic # (or mass) = highest priority )

Sequence directly attached atom first; if two are identical move on to the next

multiple bonds count as the appropriate single bonds

Put lowest priorit atom at back then look at order of priority — if clockwise, (R), if counterclockwise (S)

Diastereoisomers

stereoisomers that are not enantiomers — enantiomers are chemically identical but other times of stereoisomers may be chemically (and physically different) ex. geometric isomers

can arise in compounds with multiple stereocenters

only one stereocenter is inverted

number of possible stereoisomers for a molecule with n stereocenters

2ⁿ

meso compound

a molecule that contains stereogenic centers but is chiral

Electron flow

from a nucleophile (electron donor/ lewis base) to an electrophile (electron acceptor/ lewis acid)

nucleophiles/Lewis bases

Electron rich species that donate electrons

typically negatively charged or neutral species w a pair of electrons they can donate

most common are neutral and contain a non-bonding lone pair of electrons on a heteroatom (O, N, S, P)

neutral carbon nucleophiles

usually have pi bonds as a source of electron density

Electrophiles/ Lewis acids

Electron deficient species

can be neutral or positively charge with either an empty atomic orbital or a low lying anti bonding orbital (pi* or sigma*)

what does a curly arrow represent

the movement of a pair of electrons and most importantly the direction of displacement

Rules for curly arrows

1. the tail of an arrow begins at a lone pair or bonding pair

2. the head of an arrow ends at an atom or between atoms, generating a lone pair or single bond

3. the movement of electrons cannot create or destroy charge