Chapter 9 Flashcards
nucleophilic substitution refers to any reaction in which an electron rich … replaces a …
nucleophile; leaving group
the leaving group can be a …. or another … group that can form a … or another stable species
halide; electronegative group; stable anion
if the nucleophile is negatively charged (e.g. OH-), in a substitution rxn, the atom donating the pair of electrons (i.e. Nu) becomes … in the product
neutral
if the nucleophile is uncharged (e.g. NH3) in the sub rxn, the atom donating the pair of e- becomes … in the initial product
positively charged
a fundamental difference between SN2 and SN1 rxns is the timing of … between and the leaving group and of … between C and the nucleophile
bond breaking; bond forming
for SN2, bond breaking and bond forming occur … Thus departure of the leaving group is … by the incoming nucleophile
simultaneously; assisted
S in SN2 stands for …, n for … and 2 for a …
substitution; nucleophilic; biomolecular rxn
SN2 is bimolecular because the haloalkane and nucelophile are involved int he
rate-determining step
mech for SN2 rxn: make a new bond between a nu and an electrophile and simultaneously break a bond to give stable molecules/ions: the nucleophile attacks the reactive center from the side … the leaving group; that is, an SN2 rxn involves … attack of the nu.
opposite; backside
backside attack by the nu is facilitated through the … of the C-Lv bond, by which the C has a … charge and therefore attracks the electron rich nu. Secondly, the electron density of the nucleophile entering from the backside assists in …, thereby helping the Lv to leave
polarization; partially positive; breaking the C-Lv bond
the electron density of the nu attacking from the backside can be thought of as populating the … of the C-Lv bond, weakening that bond as the new C-Nu sigma bond becomes … Therefore, upon collision with a nu, the most effective way to fill this orbital is by collision from the … of the C, which … the C-Lv bond on the other side of the C
antibonding molecular orbital; stronger; backside; breaks
for an Sn1 rxn, bond breaking between the C and Lv is entirely … before bond forming with the nucleophile begins
completed
in the designation Sn1, 1 stands for a … rxn. This is because only the … is invovled in the rate-determining rate
unimolecular; haloalkane
For SN1, the nucleophile is also the …, hence the name …
solvent; solvolysis
mech for SN1:
- break a bond to give stable molecules/ions: ionization of the C-Lv bond forms a … intermediate. because no nu is assisting the departure of the halide anion, this is the relatively …, … step of the rxn
- make a new bond between a nucleophile and an electrophile: rxn of the carbocation with the nucleophile occurs, and can yield a positively charged species. attack of the nu occurs with approximately equal probability from either … of the planar carbocat. intermediate
- take a … away to make the species neutral
carbocation; slow; rate-determining; face; proton
in an sn1 rxn, the rate-determining step is the cleavage of the … to form a carbocation intermediate
C-Lv bond
when one of these collisions between the solvent molecules and the haloalkane is of high enough E to distort the haloalkane into a geometry in which the bond to the leaving group is almost …, the transition state for departure of the leaving group can be achieved and the Sn1 mech is enabled
completely broken
an Sn2 rxn involves a … step and therefore has no …
single; intermediates
an Sn1 rxn has … steps (or … steps when a … as the last step), each with a … Importantly, an intermediate carbocat is formed
two; three; proton is removed; transition state
those rxns whose rate is dependent only on the concentration of haloalkane are classified as …; those rxns whose rate is dependent on the concentration of both haloalkane and nucleophile are classified as …
Sn1; Sn2
because the transition state for formation of the carbocation intermediate in an SN1 mechanisms invovles only the haloalkane and not the nucleophile and this step isr ate-determining, it is a … process. the result is a … rxn. In this instance, the rate of rxn is expressed as the rate of … of the starting material. the rate has no dependence on the concentration of the
unimolecular; first-order; disappearance; nucleophile
we can conclude that any substitution rxn whose rate depends only upon [R-Lv] proceeds via an
Sn1 mechanism
For Sn2, both species must collide and are present in the transition state; that is, the rxn is … and is …
biomolecular; second order
when the rate of a substitution rxn depends on both [R-Lv] and [Nu-], we conclude that an … mechanism is occurring
Sn2