O Chem Exam 2

REDEMPTION RAHHHHHHHHH

Rules for determining IUPAC name for alkanes

Rules for determining IUPAC name for alkanes

1. find the longest carbon chain (parent chain

2. number the parent chain so you have the most possible substituents and all the substituents have the lowest possible number

3. name the chain- alkane names should be in alphabetical order, all substituent names should end with -yl (exceptions), assign numbers for substituents so that the first substituent has the lowest number

How do you determine which parent chain to choose if there are multiple possible chains with the same length

choose the chain with the most substituents

What to do if there is a tie when naming subtituents

second substituent should also have the lowest number, if there is still a tie the first substituent alphabetically gets the lowest number

when is a prefix used

when there is more than one of the same substituent in a chain

How to name bicyclic compounds

1. count the carbons in the bicyclic compound

2. number the 3 pathways from smallest to largest'

3. place the pathway numbers in brackets

4. Example: (substituents first) bicyclo [2,2,1] heptane

anti staggered confirmation in Newman projection

methyl or other groups on opposite ends of newman projection

eclipsed conformation in Newman Projections

molecules attached to second C are directly behind and almost hidden by molecules in front attached to first C

gauche conformation in Newman Projections

methyl or other groups on the same side of newman projection

Is a higher energy or lower energy newman projection more stable

lower energy newman projection

what conformation has the lowest energy

anti staggered conformation

what conformation has the highest energy

eclipsed conformation

wedge

up

dash

down

How to draw chair conformation

each C has an axial and equatorial position, the alternate around the ring

If no stereochemistry is given what is the more stable positioning of substituents

equatorial

when stereochemistry is given

substituents should maintain the given sterochem, up stays up, down stays down

Cis

substituents are pointing in the same direction

Trans

substituents are pointing in opposite directions

How to draw most stable chair conformation

Equatorial is more stable than axial

1. draw both possible conformations

2. count number of axial vs equatorial

3. if one has greater number of equatorial it is more stable, if no…

4. the one with the largest substituent in the equatorial position it is most stable

stereoisomers

have the same molecular formula, different 3D arrangement

Chiral

not identical to mirror image, have a chiral center

Achiral

identical to mirror image, no chiral center

How to determine chiral center

the chiral center has 4 different connected functional groups, no double bonds

entantiomer

mirror image of a chiral compound

How to R and S configuration

1. assign priority to all 4 groups at each chiral center

2. Rotate the molecule so the functional group with the lowest priority is behind

3. determine if rotation is clockwise or counterclockwise

How to assign atom priority

atom priority is determine by atomic number, higher atomic number higher priority

Chain rule

way of determining priority between two chains, go down chains and find difference with higher atomic number

If lowest substituent is on a wedge

flip molecule to determine RS configuration. You can also determine configuration of original molecule then go in the opposite direction ( if the original molecule with lowest substituent on a wedge has a confirmation of R, then the opposite would be S)

specific rotation equation

[a]= observed rotation/conc of sample x length of sample

a= specific rotation

enantiomerically pure

a pure chiral compound with only on enantiomer present

Racemic mixture

mixture of parts of each enantiomer

% ee equation

% ee= observed rotation/rotation of pure enantiomers

diastereomers

not mirror images, at least one chiral center with same configuration

Meso compounds

achiral but have chiral centers due to having a plane of symmetry, compounds can be divided into equal halves

Fisher Projections

highlights the chiral centers of a compound

intersections= chiral center

horizontal lines= wedge

vertical lines= dash

Enthalpy (ΔH)

measure the exchange of kinetic energy between system and surroundings

How to determine ΔH

amount of energy to break a bond (BDE- bond dissociation energy)

total change in enthalpy for a reaction to break bond

ΔH rxn + BDE

total change in enthalpy for a reaction to form bond

ΔH rxn - BDE

Exothermic

system gives energy to surroundings (ΔH = -)

Endothermic

system gains energy from surroundings (ΔH = +)

Entropy (S)

the measure of the disorder associated with a system

Increase in entropy (ΔS_tot = +)

spontaneous

Decrease in entropy (ΔS_tot = -)

non-spontaneous

equation of change in entropy

ΔS_tot= Δ_sys + ΔS_surr

Gibbs free energy (ΔG)

way of expressing total energy

-ΔG

spontaneous

+ΔG

non-spontaneous

Gibbs Free Energy equation

ΔG= ΔH - TΔS

ΔH

associated with the change in entropy of surroundings

ΔS

associated with the change in entropy of system

K_eq

equilibrium constant

equilibrium equation

K_eq = Products/Reactants = [C][D]/[A][B]

When K_eq > 1

reaction favors products and ΔG is -

When K_eq < 1

reaction favors reactants and ΔG is +

equation that relates K_eq and ΔG

ΔG= -RTlnK_eq

Kinetics

study of the rates of reaction

(k)

rate constant

general rate equation

rate= k[A]^x[B]^y

first order

rate= k[A]

second order

rate= k[A][B]

third orderk

rate= k[A]²[B]

What 3 factors the value of rate constant depends on

1. energy barrier between reactants and products, lower E_a= faster reaction

2. raising temperature will increase reaction rate

3. the orientation and geometry of reactants will impact frequency of collisions- more frequent collisions = higher rate of reaction

Catalyst

compound that can speed up rate of reaction without being used up

thermodynamics

tells us about the equilibrium concentrations of reactants and products

Higher activation energy

higher energy product= thermodynamically favored= slower reaction

Lower activation energy

lower energy products= lower activation energy= kinetically favored= faster reaction

reaction ran at high temp

high temp= higher activation energy= lower energy product= thermodynamically favored= slower reaction

reaction ran at low temp

low temp pathway= lower activation energy= higher energy product= kinetically favored= faster reaction

transition states

peaks on energy diagram

intermediates

valleys or dips on energy diagram

nucleophiles

electron rich center, characterized with a positive or paritial positive, have the ability to donate a pair of electrons

electrophiles

electron deficient, characterized by the ability accept a pair of electrons

nucleophile attack reaction

nucleophile “attacks” electrophile and forms a bond by donating a lone pair to electrophile to form bond. Usually a 1 arrow movement but may be 2 when a double bond must be moved or broken to form a bond

loss of leaving reaction

bond is broken between group and more electronegative/nucleophile giving the nucleophile a negative charge and the group a positive charge

Proton transfer reaction

think of an acid-base reaction process, a proton is transferred from nucleophile to electrophile, and takes a hydrogen other molecule in return, usually a 2-arrow movement could be more

Increasing stability of carbocations

methyl (3 H connected to C) < Primary carbocation (2 H connected to C, 1 alkyl) < Secondary carbocation (1 H connected to C, 2 alkyl) < Tertiary Carbocation (0 H connected to C, 3 alkyl)

Hydride shift

H shifts from one side to the other, make a secondary carbocation into a tertiary carbocation

methyl shift

methyl shifts to other side of molecule to turn secondary carbocation into tertiary carbocation