Ch. 21: Organic Chemistry II: Reactions Flashcards
define synthesis
the process of making compounds in one or more steps
define resonance effect
the stabilization of a chemical species through pi delocalization
define inductive effect
the through-bond donation or withdrawal of electron density
define carbanion
a chemical species that contains a carbon atom with a formal negative charge
define hydrogenation
the catalyzed addition of hydrogen to alkene double bonds to make single bonds
define interconversion
functional group transformation
define nucleophile
a chemical species that can donate electrons to an electrophilic site on another molecule, leading to bond formation
define leaving group
the group that is removed from a substrate in a substitution reaction
define substrate
the reactant molecule in a biochemical reaction that binds to an enzyme at the active site
define electrophile
a molecule that contains an atom with a positive charge which can accept electrons from another molecule, such as a nucleophile
define carbocation
a chemical species that contains a carbon atom with a formal positive charge
define racemization
the loss of stereochemical purity in a chemical reaction, such as in SN1 substitutions
define nucleophilicity
a measure of the effectiveness, or strength, of a nucleophile
define 1,2 elimination
the loss of atoms or groups, bonded to adjacent carbon atoms in alkane, yielding an alkene
define dehydration
the elimination of water from an alcohol to yield an alkene
define dehalogenation
the elimination of HX from an alkyl halide to yield an alkene
define Zaitsev’s rule
when isomeric alkenes are produced in an elimination reaction, the major product is usually the most substituted alkene
define oxonium ion
a chemical species in which an oxygen atom carries a formal positive charge
what is Ka
a measure of acid strength
as electron affinity increases acidity ____
increases
the higher the pKa the ___ acidic the chemical is
less
a chemical effected by induction has a ____ acidity than a very similar chemical that is not effected by induction
greater
the inductive effect is a result of ____ ____ that polarize other bonds in the atom
bond dipole
is it possible for the inductive effect to effect bonds that are many bonds away from the electronegative atom and its resulting dipole?
yes
if the conjugate base is resonance stabilized the acid becomes ____
stronger
why are the pKa values of alkenes very high?
because the charge is completely localized on a carbon atom and there is no additional stabilization of the charge
what is a mechanism?
an attempt to represent a reaction at a molecular level, in a step-by-step manner
acid=…?
electron pair acceptor
base=….?
electro pair donor
the conjugate acid with the highest pKa results in the ____ base
strongest
to react with an acid, a base must have a conjugate acid that has a pKa ___ than that of the reactant acid
higher
Oxidation involves the ____ of electrons
loss
Reduction involves the ____ of electrons
gain
what are the three rules for determining the oxidation state of an atom?
(1) each bond to an atom that is LESS electronegative is counted as -1 toward the oxidation state
(2) each bond to an atom that is MORE electronegative is counted as +1 toward the oxidation state
(3) bonds to the same type of atom are not counted
to determine wether electrons have been lost or gained we examine the changes in ____ _____
oxidation state
the reduction of an organic molecule usually involves the addition of a _____
hydrogen
if the change in oxidation state is -2 what does this mean about the loss or gain of electrons?
it means a gain of two electrons
if the change in oxidation state is negative the atom has be ____
reduced
if the change in oxidation state is positive the atom has be ____
oxidzed
hydrogenantion and reduction are ____ terms
equivalent
primary alcohols are oxidized to ____
aldehydes
secondary alcohols are oxidized to ____
ketones
what are the two principle mechanisms for nucleophilic substitutions at saturated carbons?
SN1 and SN2
the formation of the carbocation intermediate in a SN1 reaction is most likely to occur if the carbocation is _____ by the structure of the substrate
stabilized
the second step in the overall SN1 reaction ____ (is/is not) the rate determining step
is not
the first step in the overall SN1 reaction ____ (is/is not) the rate determining step
is
racemization occurs in a SN1 reaction because…?
if the substrate is originally a chiral center it will become a trigonal planar molecule and then when then the nucleophile attacks it could become either R or S configuration
what is the effect of the inversion that occurs during and SN2 reaction/
the carbon atom switches fromR to S configuration or vice versa
a good nucleophile will cause an SN2 reaction to occur ____
quicker
a good nucleophile causes ____ in the rate of a SN1 reaction
no change
the best leaving groups are…?
the conjugate bases of strong acids
what is the citerion for a good leaving group?
the leaving group must develop and accept a negative charge and the corresponding ANION being very STABLE
for Sn1 reactions what greatly affects the rate of the reaction
the stability of the carbocation reaction intermediate
what does the stability of a carbocation depend on?
the number of alkyl groups bonded to it
stability of a carbocation increases with ____ number of alkyl groups bonded to it
increasing
in Sn2 reactions, the rate is affected by ____ ___
steric hinderance
methyl and primary substrates ___ undergo Sn1 substitutions
never
tertiary substrates never ____ undergo Sn2 substitution reactions
never
steric hinderance is a result of the ____ between the alkyl groups on the substrate and the nucleophile
repulsion
dehydration reactions occur in the presence of…?
a strong acid and heat
dehalogenantion reactions often require the prescence of…?
a strong base and heat
why do many elimination reactions give mixtures of products?
because there are often two or more elimination sites around the -X or -OH groups
if a weak based is used an elimination reaction will likely occur via an _____ mechanism
E1
E2 mechanisms generally require a ___ base
strong
the E1 mechanism does not generally occur in ____ alcohols or ____ alkyl halides
primary
primary
what carbons centers can E2 eliminations occur on?
primary, secondary and tertiary
bases are also ____ which causes both elimination and substitution reactions to occur
nucleophiles
as a general rule a strong bases favours ___ over ___
elimination over substitution
