Test 1 Flashcards by Dylan Johnson

constitution

difference in atom connectivity

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configuration

difference in atom spacious arrangement. asymmetric centers. R/S

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conformation

different in shapes, no bond breaking. cis-trans and Z/E

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optical rotation formula

[a]=100a/cl

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enantiomeric excess formula

%major-%minor enantiomer = a/[a]

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optical rotary dispersion

measurement of rotation as a function of wavelength

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circular dichroism theory

differential absorption of circularly polarized light. expressed as molecular ellipticity (/) nought

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CD equation

(/)=3330(epsilon_L - epsilon_R)

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epimeric

positions in two diastereomers that have different configuration

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epimerization

changing the configuration at a stereogenic center

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erythrose

chiral substituents are on the same side in fischer projection

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D vs L

L designates left direction of priority group when written as fischer projection when most oxidized group is oriented at top

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maximum number of diastereomers

2^n with n stereogenic centers

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prochrial centers

has two identical ligands, that are heterotropic if the two other ligands are different.

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enantiotopic

Two positions of identical ligands on a prochiral center are called enantiotopic

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a stereoheterotopic face of a trigonal atom is designated “Si” if the ligands of the trigonal atom appear in a ? direction

counterclockwise

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3 ways to isolate enantiomers

resolving agents (generates products with separable characteristic), chromatographic (chiral stationary phase), kinetic resolution (utilizes difference in reaction rates)

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conformational analysis

process of relating conformation to the properties and reactivity of molecules

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what is the main factor responsible for the torsional barrier in ethane

hyperconjugation. hydrogens are not close enough for van der waals repulsion(aka steric effect)

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propene favors eclipsed conformation due to ?

1,3-allyl strain

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why do substituents prefer equatorial position in cyclohexane

steric effects: gauche and van der waals (1,3-diaxial)

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cis vs trans decalin stability difference

cis is less stable due to inter ring gauche and cross ring axial hydrogen interactions

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strain energy in 8-12 member rings due to ?

cross ring vanderwaal

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stereoselective

two different stereoisomers proceed to form same same stereoisomer

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total strain energy formula

E=E(r, stretch) + E((/), angle) + E(torsional) + E(d, nonbonding)

regioselectivity

preference to bond to specific atom

standard enthalpy of formation, delta H_f

enthalpy of the compound relative to the reference state of its constituent elements. independent of the process by which the compound is formed, meaning it is additive and can be precisely calculated

reference enthalpy for H, N, O, and F

gaseous diatomic molecule form

reference enthalpy for carbon

graphite. consists of only sp2 carbons

chain branching increases/decreases stability of alkanes

increases

substitution on the double bond stabilizes/destabilizes alkenes

stabilizes

why is direct comparison of delta H_f not meaningful for stability comparison

reference points are different

homolytic BDE

energy required to break a single bond where one electron goes to each atom

enthalpy of reaction equation

deltaH=deltaH_f,products-deltaH_f,reactants=BDE_bonds broken - BDE_bonds formed

C-C, N-N, O-O BDE trend

C>N>O

F2, Cl2, Br2, I2 BDE trend

F2Br2>I2

NH, CH, OH, HF BDE trend

C-H bond BDE trend

methane>primary>sec>tert>benzylic and allylic

transferable group equivalents method

molecule is divided into its component groups and the enthalpy of formation is the sum of the groups

problem with transferable group method

doesn't consider long range nonbonded interactions. also group equivalents refer to strain free molecules, although can be refined by incorporating nonbonding interactions (ex. gauche)

Molecular mechanics methods for calculating deltaH_f

MM4 most common. uses iterations to locate energy minimum. grounded in experimental measurements on a limited number of molecules. takes molecular geometry into account

MO and DFT calculations

semiemperical and ab initio

transition state theory

reaction is assumed to involve the attainment of an activated complex that goes on to product at an extremely rapid rate

plot ln(k_r/T) vs 1/T, slope equals:

-deltaH^dd/R

exothermic delta H

negative

more disorder entropy

postive

magnitude of enthalpy^dd change for concerted reactions where bond making accompanies bond breaking

low deltaH

magnitude of entropy^dd change for pericyclic transition. state. why?

large negative entropy. measures degree of re-organization

entropy is related to changes in ?, ? and ? degrees of freedom

translational, vibrational, rotational

enthalpy^dd magnitude if 2sigmas break and 1pi forms

large positve

entropy^dd magnitude if 2sigma break and 1pi forms

large postive

A + B > C + D reaction energy profile

SN2

A > B + C > B + C + D > E + F reaction energy profile

SN1 in solvent D

A + B <> C > D + E > D + E + F > G + E reaction energy profile

acid catalyzed ionization where F is halogen

function of two dimensional energy diagram

shows multiple reaction pathways to product. ex. associative, dissociative, concerted

conditions for thermodynamic control in reaction of ketone to enolate

base weaker than enolate or protic solvent

bell evans polyani relationship

E_a=E_o + a*deltaH where E_o is activation energy of reference reaction

hammonds postulate

early transition state, structure resembles reactants. late transition state, structure resembles products

Curtin–Hammett principle

for a reaction that has a pair reactants that interconvert rapidly, each going irreversibly to a different product, the product ratio will depend both on the difference in energy between the two conformers and the free energy of the transition state going to each product

three types of substituent effects

electronic, steric, structure specific

three types of electronic substituent effects

delocalization, polarity, polarizability

two types of delocalization substituent effects

resonance, hyper conjugation

two types of polar substituent effects

field, inductive

classify steric substituent effect

non-bonding interactions

electronegativity trend

F=4.0, decreases by 0.5 to left and down

allred and rochow electronegativity uses ? in calculation

z_eff (effective nuclear charge)

Allen's ? scale for electronegativty

spectroscopic

Mulliken's ? electronegativity

absolute

original pauling EN equation

BDE_AB=(1/2)(BDE_AA + BDE_BB) + 23(deltaEN)^2

What does sanderson's group electronegativity tell us

electron density will reach an equil state in which there is no net force on the electrons

hybridized carbon EN trend

sp > sp2 > sp3

bond strength is increased/decreased by EN differences

increased

polarizability measures ?

response to an electric field

hardness decreases/increases w/ electric field

increases

larger HOMO-LUMO gap increases/decreases hardness

increases

smaller ions are softer/harder than heavier ions

harder

hard-hard interaction dominated by ?

electrostatic attraction

soft-soft interaction dominated by ?

mutual polarization

polarizability increases/decreases with atomic radius

increases

polarizability increases/decreases with nuclear screening

increases

polarizability trend of ethane, ethene, and ethyne

ethane > ethene > ethyne

refractive index

how much the speed of light is decreased by a medium

polarizability is the sum of ?

dipole moment vectors

benzene polarizability is weakest/greatest perpendicular to the plane

perpendicular

stable resonance structure qualitites

max # of bonds, minimal charge separation, charge distribution consistent with relative EN

purpose of resonance

interpret stability due to conjugation and delocalization

covalent radius

distance between two bound atoms

van der waals radius

nonbonded radius of an atom. distance where nonbonded atoms begin to experience mutual repulsion

stereoelectronic component of hyperconjugation

antiperiplanar alignment of donating electrons with pi* orbital

anomeric effect

preferred axial position at anomeric carbon in pyranose rings. lengthens C-O bond and shortens substituent bond

covalent radius trend of hybridized carbons

sp3>sp

MO method that uses fewest approximations

abinitio

MOs are described as LCAOs. what does LCAO stand for

linear combination of atomic orbitals

in huckel MO method, only adjacent ? orbitals interact

p_z

energy levels for conjugated linear polyenes and conjugated monocyclic polyenes using huckel MO method

E=a+mB

What info does HMO give

frontier orbitals, shape and composition, homo-lumo gap, overall stabilization from conjugation and delocalzation

3 criteria of aromaticity

energy, structural, electronic

approaches for electronic criteria

experimental (thermodynamic measurements of bond energies that are additive when there are no special interactions) and computational

isodemic reactions

number of each kind of bond is the same on each side of reaction

aromatic compounds exhibit a paramagnetic/diamagnetic current

diamagnetic

Nuclear independent chemical shift value for aromatics

negative

aromatic compounds effect on magnetic susceptibility

enhanced

annulenes

completely conjugated monocyclic polyenes

bond length alternation falls under which criteria for aromaticity

structural

aromatic systems are maintained if sp2 is replaced with ? or ?

N or O^+

2,3-benzene fused rings are more/less stable than 3,4

ortho para directors are ERG/EWG

ERG

EWG are activating(ortho-para)/deactivating(meta)

deactivating

why does resonance weaken down the ptable

greater bond distance and less orbital overlap

hammett equation relates ? with ?

rates with equilibrium constants

electron donating groups increase/decrease acidity of benzoic group in para position

decrease

hammett relationship relates substituent to ?

acidity

hammett equations

log(K/K_0)=sigma * p , log(k/k_0)=sigma * p

Test 1 Flashcards

(113 cards)