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 ____