chem 235 exam 2

Enantiomers

A pair of molecules who are "Nonsuperimposable" mirror images

Diastereomers

A pair of molecules who are "nonsuperimposable" NON-mirror images

E. only A and C

Enantiomers are

•Angle strain

Happens when the actual molecular bond angles are different than the ideal bond angles

B. 2 *first and last one

How many are constitutional isomers of each other?

C. 3 1, 3 and 5

How many are diastereomers?

B. 2

How many chiral centers?

0. 2 2. 2

How many chirality centers are in each of the following compounds?

reactants products

according to the Hammond Postulate transition states in exo rxn resemble ___ and endo rxn resemble ___

Loss of a Leaving Group

heterolytic bond cleavage, an atom or group takes the electron pair

top one: non enantiomers (mirror images but superimposable) bottom one: enantiomers (mirror images, non superimposable)

how are the molecules related

Intermediates

is an intermediate species formed during the course of a reaction. They are energy minima •are observable. They are an actual chemical species that exists for a period of time before reacting further

cis

prefix used when 2 groups are on same side of ring

stereoisomers

same connectivity, different spatial arrangement

Catalyst

speeds up the rate of a reaction without being consumed enzymes are ____ provides an alternate, and faster pathway of rxn lower Ea

exergonic

-an equilibrium will eventually be reached -A spontaneous process means there will be more products than reactants -The greater the magnitude of a (-)ΔG, the greater the equilibrium conc. of products

Nucleophilic Attack

1.may require more than one curved arrow •The alcohol (nucleophile) attacks a carbon with a δ+ charge. • The second arrow could be thought of as a resonance arrow.

ring strain

ANY combination of the 3 basic types of strain occurring in a ring system

•Steric strain

An energy increase caused by electron repulsion between non-bonded atoms or groups of atoms that occupy the same space

•Torsional strain so whenever the molecule is doing conformational changes, that's basically torsional strain

An energy increase due to the repulsion between electrons in eclipsed bonds Has to do with molecules changing conformations

b. Different drawing of the same compound.

Are the molecules below a pairs of constitutional isomers or the same compound?

a. No

Are these two molecules superimposable?

Activation Energy (Ea)

As ______ increases, the number of molecules possessing enough energy to react decreases •The lower the ___________-, the faster the rate

D. 4 * the one with the c=o is not one

How many of the below are constitutional isomers?

A. 1 only C

How many pairs of enantiomers?

D. B is the energy of activation, C is the difference in free energy, exergonic

Identify B and C and determine whether the reaction is endergonic or exergonic as drawn.

e. 4, 7, 8

Identify all the chirality centers in the molecule.

C. D and G

Identify the electrophilic centers in the following molecules.

D. A, C, E, F and H

Identify the nucleophilic centers in the following molecules.

D. 5 *has 2^5 = 32 different compounds(isomers)

Identify the number of chirality centers in the molecule.

A. plane of symmetry C.no D. not a meso compound

Is this compound a meso compound?

false Achiral molecules that have stereocenters (chiral centers) are called "meso compounds"

T or F? All molecules with stereocenters (chiral centers) are chiral.

E. Any of the above strains *any combo of them

What causes ring strain?

E. C and D

What is a chiral center?

A. R

What is the configuration?

B. 2-methylhexane

What is the correct IUPAC name for the following structure?

D. 5-chloro-2,2-dimethylheptane

What is the correct IUPAC name for the following structure?

e. 7-chloro-3-methyldecane 3+7 is lower than 4+8 and ABC order

What is the correct IUPAC name for the following structure?

C. A and C **E:methyl-pentane

What is the correct structure(s) for hexane?

D. 3

What is the maximum number of methyl groups that can be in the equatorial position at the same time?

B. enantiomers

What is the relationship between the following molecules represented in their Fischer projections?

e) C and D

What is the relationship between the molecules?

B. configurational isomers

What is the relationship between...

D. the same molecule

What is the relationship between...

E. A and B mirror nonsuperimposable (rotate flat drawing=not the same)

What is the relationship between...

E. A and B mirror image, nonsuperimposable

What is the relationship between...

A B is angle strain C is steric strain

What is torsional strain?

A. molecule (a)

Which Fischer projection below corresponds to this molecule?

B. C * A and B are same if you flip

Which are constitutional isomers of A?

A

Which are diastereomers?

C. C+D are thermodynamic and kinetic

Which are the kinetic products and which are the thermodynamic products?

D. all of the above

Which is true about diastereomers?

A. B *A and C are same so not const. isomers

Which is/are constitutional isomers of A?

E. all of the above

Which of the following are true about:

D. 4

Which of the following cyclic structures is the most stable?

A. 1 methyl groups run into each other

Which of the following disubstituted hexane structures is the least stable conformation shown?

D. A and C

Which of the following have a negative ∆S?

d. b, f, g, h a=trans b=cis c=neither d=trans e=neither f=cis g=cis h=cis

Which of the following represent cis isomers?

B. 1 and 3

Which of the following will be spontaneous?

B

Which represents the chair conformation of the following with both groups axial?

E OH is left to M

Which represents the ring flip of the structure?

B

Which statement is true?

D. A & B

Which types of strain does cyclopropane have?

higher

____ temp results in fast rxn at ____ temp moelcs have more KE/more molecs will have enough E to produce a rxn

chiral

term used to state that a molec does have an enantiomer in other words a mole -has a mirror image -that is nonsuperimposable

meso compound

those molecules who HAVE chiral centers... but aren't chiral (because of a plane of symmetry that passes through the molecule).

kinetics: rate of rxn thermodynamics: equilibrium

what is the diff bt kinetics and thermodynamics

enantiomers nonsuperimposable mirror images chiral carbon stereocenter OFTEN but not always, enantiomers have a chiral center

what is the relationship bt these molecules

Constitutional Isomers

what kind of isomers?

exothermic

• The energy gained by bonds formed exceeds the energy needed for bonds broken products more stable than reactants • Products lower in energy • Energy is released as heat (PE converted to KE) • DH˚ is negative • Temp of surroundings increases

transition states

• is the high energy state a reaction passes through •are fleeting; they cannot be observed •are energy maxima, and represent the transition as bonds are made and/or broken

endothermic

•Energy needed for bonds broken exceeds the stability gained by the bonds formed products less stable than reactants • Products higher in energy • Energy is consumed (KE converted to PE) • DH˚ is positive • Temp of surroundings decreases

Entropy (ΔS)

•Exothermic and endothermic reactions can occur spontaneously (most reactions are exothermic though) •can be described as molecular disorder, randomness, or freedom •is actually the number of vibrational, rotational, and translational states the energy of a compound is distributed.

•Configurational isomers can't be interconverted simply by rotation around single bonds (or ring flips) •In order to convert between configurational isomers, we must break bonds and reattach atoms in their "new" positions". •Configurational isomers are actually different molecules from each other.

•How are configurational isomers different (from conformational isomers?)

cis trans cis. neither trans

•Identify the following as either cis, trans, or neither.

ID ID SI SI CS

•Identify the following pairs as either constitutional isomers, stereoisomers, or identical structures

Electrophile

•electron deficient species, can accept a pair of electrons • are Lewis acids •Carbocations and partially-positive atoms

Nucleophile

•electron rich species, can donate a pair of electrons -Nucleophiles are Lewis bases -More polarizable = stronger ____