CHEM MIDTERM 2

constitutional isomers

have the same molecular formula, same index of hydrogen deficiency

calculate IHD

1/2(2C +2 +N -H-X)

how to tell if a molecule is completely saturated

maximum hydrogens present, CnH2n+2

configurational isomers

are stereoisomers, have same connectivity but differ in ways other than rotation about single bonds.

enantiomers are

mirror images of each other, cannot be superimposed

a molecule is chiral if it has

an enantiomer

a molecule is achiral it

doesnt have an enantiomer

a molecule that has at least one plane of symmetry

is achiral

stereocenters

are carbons bonded to four different groups or two different groups and c=c double bond

chiral centers

are carbons that are bonded to four different groups, resulting in non-superimposable mirror images.

exchanging any two substituents attached to a chiral center with a given configuration

results in the opposite configuration

molecules with exactly one chiral center

must be chiral

a molecule is meso if

it contains at least two chiral centers but has a plane of symmetry that makes it achiral

in enantiomers every chiral center having one configuration in one enantiomer must

have the opposite configuration in the other enantiomer.

diastereomers

configurational isomers that are not mirror images of one another

absolute configuration R/S

identifies the specific arrangements of substituents in space on chiral centers

clockwise abs config

R

counter clockwise abs config

S

determining priority on atoms with double/triple bonds

treat each bond separately as if there are two or three atoms connected to main carbon

if a molecule and its mirror are able to interconvert than

the molecule is achiral

determining chirality in chairs

do not need to consider which chair, instead analyze the substituents' arrangement on the cyclohexane.

nitrogen inversion

uncharged nitrogens (N with 3 bonds lone pair) rapidly interconvert in sp2 and sp3 hybridization, they are not chiral centers

cis and trans isomers are examples of

diastereomers

characterizing absolute double bond configuration (Z/E)

Z is priority groups on same sides, E is priority groups on opposite sides

if two isomers are the same by reversing the configuration of some but not all chiral centers

they are diastereomers

if two isomers are related by reversing all chiral centers

they are enantiomers

the maximum number of configurational isomers that exist for a molecule

is 2^n where n is the number of chiral centers.

constitutional isomers must have ______ properties

different physical and chemical

enantiomers have the same chemical and physical properties in

achiral environments

enantiomers have different chemical and physical properties in

chiral environments

diastereomers have ____ properties

different physical and chemical

how to separate enantiomers

create a chiral environment, ie chiral chromatography

turn the enantiomers into diastereomers temporarily

enantiomers interact differently with

plane polarized light

polarized light is

all photons from a light sources have their electric fields oscillating in the same plane

polarimetry

plane polarized light enters a tube containing compound of interest, and rotation of plane of polarized light is measured to determine optical activity

enantiomerically pure chiral compounds are

optically active because they rotate the plane of polarization in right (+) or left (-) direction

achiral compounds leave the plane

unchanged, they are optically inactive

chiral compounds that rotate light (+) are called

dextrorotatory

chiral compounds that rotate light (-) are called

levorotatory

the angle of rotation is dependent on

the concentration of the compound and the path length of the light.

a racemic mixture

contains equal amounts of (+) and (-) enantiomers

racemic mixtures are optically

inactive because the rotations of the enantiomers cancel each other out.

measured rotation

(%ee)(specific rotation of pure enantiomer)/100

proton transfer reaction

chemical reaction involving the transfer of a proton (H⁺) from one molecule to another, resulting in the formation of an acid and a base.

bronsted lowry acid base

acid- H+ donor

base- H+ acceptor

formal charge on acids

decrease by one

formal charge on bases

increase by 1

concerted reaction

all changes occurring in the reaction happen simultaneously

reaction favors side

with the weaker acid

lower pka

stronger acid

stronger base has

a weaker conjugate acid

a weaker base has

a stronger conjugate acid

leveling effect

the strongest acid that can exist in solution is the pronated solvent

the strongest base that can exist in solution is the depronated solvent

le chateliers principle

a reaction at equilibrium will shift to counteract changes in volume, concentration, temp and pressure

pH measures

how much H30 is in solution, how strong an acid is

lowering ph of a solution will

shift reaction toward reactants

increasing ph of a solution will

shift reaction toward products

HA will be dominant form when

ph of a solution is lower than the pka of HA

A- will be the dominant form when

ph of solution is higher than pka of HA

henderson hasselbach equation

is an equation used to calculate the pH of a buffer solution. It relates the pH to the pKa and the concentrations of the acid and its conjugate base.

when pH is > pKa

then log[A]/[HA] must be positive, A> [HA]

when pH <pKa

then -log[A/HA] must be negative, A < [HA].

gibbs free energy

thermodynamic potential of an equation, relationship between enthalpy and entropy, determines reaction spontaneity

lower delta G means

more stability

exergonic

delta G negative, release of energy

endogonic

delta G positive, requires input of energy

reaction coordinate

x axis on free energy diagrams, represents the stage of progression of the reaction

activation energy

The minimum energy required for a chemical reaction to occur, represented by the energy barrier that must be overcome for the reactants to form products.

delta g naught double dagger

The standard free energy of activation, which indicates the energy change necessary to convert reactants into activated complexes.

height of the energy barrier

corresponds to how long the reaction takes

Keq>1

reaction favors products, more reactants turned into product

Keq <1

reaction favors reactants, more products turn back into reactants.

mathematical relationship between G and Keq

delta G = -RTlnK

two molecules with the same functional groups will

have similar pKa/pH

how to identify whether a functional group has impact on the ph

the functional group is attached to the atom being de-protonated (acid)

a proton is more acidic when

it is attached to a positively charged atom

anions become ___ stable when EN of atom bearing - charge ___

more, increases.

cations become ____ stable as the EN of atom bearing charge ____

less, increases

acid strength relating to hybridization

sp>sp2>sp3

delocalization of the charge, which stabilizes molecules by reducing electron density

resonance effect on acid strength

inductive effects

replacing H-C bond with higher EN atom-C can stabilize the charge on the anion

anions are _____ by electron withdrawing groups near the negative charge

stabilized

cations are _____ by electron withdrawing groups near the positive charge

destabilized

electron donating groups

distort electron density away, destabilizing the charge on the anion

cations are ____ by electron donating groups near positive charge

stabilized

CARDIN-al Rule

Charge>Atom>Resonance Delocalization> Inductive Effects