Quiz 4 Flashcards
Fischer projections
used to draw complex molecules (usually sugars) with multiple chiral centers
are the horizontal lines on a fichser projection dashed or wedged?
horizontal lines are wedged/ coming out of page
Are vertical lines on a Fischer projection dashed or wedged?
dashed/ going into the page
why does the reaction happen? are products more stable than reactants?
thermodynamics
how does the reaction happen? how do temperature and concentration affect the rate of reaction? How fast does the reaction happen?
Kinetics
enthalpy (H)
the exchange of energy between a system and its surroundings for any process
to calculate heat of reaction its — minus —
reactants minus products
True or false?
Most reactions will require the breaking and forming of bonds
True, think about all the reaction mechanisms you will learn
Entropy (S)
The measure of disorder within a system
using probablity and liklihood
What sign of enthalpy is favorable and nonfavorable
posititve enthalpy (endothermic)= non favorbale
negative enthalpy (exothermic)= favorbale
What sign of entropy is favorable and non favorbale?
positive entropy = favorable
negative entropy = non favorable
needs to be positive so G can be negative
What sign of G indicates a spontaneous reaction?
negative g
positive g is non spon
negative G, where products are lower energy than reactants, spontaneous
exergonic
positive g, where products are higher energy than reactions, non spon
endergonic
like how endothermic is not favorbale, neither is endergonic
Keq> 1
products are favored, reaction proceeds towards products
Keq<1
reactants are favored, reaction proceeds towards reactants
Keq = 1
rxn is at equilibrium
True or false?
Spontanenous does not mean slow!
false, spontaneous does not mean fast!
but ig it also doesnt mean the first thing
Name the four factors that can affect the rate constant
- Energy of activation
- Temperature
- Steric/ geometric orientation
- presence of a catalyst
True or false?
A catalyst can speed up a reaction by lowering the Ea by changing transition state orientation?
false! a catalyst can never lower the energy of activation
transition state
the peaks of an energy diagram, where bonds are actively being broken and formed, unstable/high energy
What can a transition state tell you about the number of mechanistic steps of a reaction?
the number of tranisition states on the graph show the number of mechanistic steps
Intermediates
certain, but short lifespan, appear on the wells of the graph, more stable/lower energy
Activation energy
the amount of energy it takes to complete a reaction, the more it takes the slower the reaction
Hammonds Postulate
- in exergonic reactions, the transition states are closer in energy to the reactants so they will structurally be more similar to the reactants
- in endergonic reactions, the transition states are closer in energy to the products so they will structurally be more similar to the products
Nucleophile
electron dense wants to give up electrons
- often negatively charged or w/ a l.p.
- double bonds (electron dense)
- lewis base
examples of nucleophiles
- halides (NOT ALKYL HALIDES)
- bases
- alcohols
- water (weak nucleophile)
electrophiles
e-deficient, accepts lone pairs
- often a positive charge
- lewis acid
examples of electrophiles
- alkyl halides
- carbonyl groups
- carbocations
Arrows starts at a place of electron — and points to a place of electron —
density, deficiency
nucleophilic attack
nucleophile attacks and attatches to electrophile
- arrow from negative charge to positive charge
Loss of a leaving group
grp skedaddles off of molecule (often a terminal halogen)
- one atom takes both e-
Proton transfer
acid/base
two arrows, proton leaves one atom and moves to another
carbocation re-arrangement
stabilizing a carbocation by moving a methyl or hydride grp to fill empty p orbital w/ electrons
True or false?
Nucleophilic attack should be drawn in before a carbocation re-arrangement?
False, a carbocation ion will stabilize with re-arragnment before attack if it can
True or false?
methyl and hydride shifts can occur with any methyl or hydride grp on a molecule?
false, it can only be adjacent methyls or hydrides
Steps to determining if a re-arrangement is right
- Identify all adjacent carbons to the carbocation
- Identify all adjacent methyl and hydride groups
- draw out methyl and hydride shift to see if either create a more stable carbocation
substitution reactions
nucleophile replaces alkyl halide on the molecule
nucleophilic attack + loss.of leaving grp
elimination reactions
reagents act as a base for a proton transfer and formation of pi bond
proton transfer + loss of leaving grp
true or false?
Substitution and elimination reactions only occur at Sp3 hybridized carbon atoms.
True, sp2 has too high of activation barrier
What are two reasons halogens promote substitution and elimination reactions?
- Halogens draw e-density away by induction creating a e- deficient place for nucleophilic attack
- alkyl halides make good leaving groups
alpha carbon
carbon directly attatched to alkyl halide
beta carbon
carbon adjacent to alkyl halide
Is the subsitution rxn more sensitive to substituents on the alpha or beta carbon
alpha carbon, but still senstive on beta carbon just not as much
at what amnt of substituents attatched to the alpha or beta carbon will the reaction no longer happen?
on a tertiaty alpha or beta carbon
Steric Hindrence
crowding of the alpha carbon by groups that are not H groups
concerted rxn
all mechanistic steps happen at one, one intermediate
stepwise reaction
more than one mechanistic step, more than one transition state
