Chapter 7: Common Elementary Steps

Question 1

A lewis base is an

Answer 1

electron pair donor

Question 2

A lewis acid is an

Answer 2

electron pair acceptor

Question 3

A spectator ion is one that is:

Answer 3

relatively inert and tends not to react in solution.

Question 4

Curved arrow notation concepts:

Answer 4

1. Opposite charges react; like charges repel. 2. Atoms in the first and second rows of the periodic table must obey the duet and octet rules, respectively.

Question 5

In an elementary step, electrons tend to flow from:

Answer 5

an electron rich site to an electron-poor site.

Question 6

In an elementary step, a lewis base tends to form a bond with:

Answer 6

a lewis acid

Question 7

Organometallic compounds contain:

Answer 7

a metal atom bonded directly to a carbon atom ex. alkyl lithium (R-Li); alkyl magnesium halide (R-MgX)

Question 8

Carbanions are:

Answer 8

compounds in which a negative formal charge appears on C

Question 9

Hydride reagents are commonly used as:

Answer 9

reducing agents

ex: LiAlH_4, NaBH₄

Question 10

What happens in an S_N2 step?

Answer 10

a substrate undergoes substitution in which one atom or group of atoms is replaced by another

a nucleophile forms a bond to the substrate at the same time that a bond is broken between the substrate and a leaving group

bimolecular because it contains two separate reacting species in an elementary step

Question 11

Leaving groups are commonly:

Answer 11

relatively stable with a negative charge

conjugate bases of strong acids

Question 12

A nucleophile tends to be attracted by and form a bond to:

Answer 12

an atom that bears a partial or full positive charge

Question 13

A coordination step is:

Answer 13

a step in which a single covalent bond is formed.

Question 14

Heterolytic step (heterolysis) is;

Answer 14

a step in which a single bond is broken and both electrons from that bond end up on one of the atoms initially involved in the bond

are the reverse of coordination steps

Question 15

A bimolecular elimination (E2) step is:

Answer 15

one in which a double or triple bond is formed in the products

can take place when a srong base is in the presence of a substrate in which a LG and a hydrogen atom are on the adjacent carbon atoms

Question 16

E2 step substrate generally has the form:

Answer 16

H-C-C-LG

or

H-C=C-LG

Question 17

A nucleophilic addition step is:

Answer 17

when a :nuc bonds to an atom that is involved in a polar pi bond; named because it ADDS to the polar pi bond

Question 18

A nucleophilic elimination is:

Answer 18

when a lone pair of electrons from a more electronegative group forms a pi bond with a less electronegative atom; a LG is simultaneously expelled and is left with a negative charge and lone pair (becomes a :nuc)

Question 19

Electrophilic Addition is

Answer 19

occurs when a species containing a nonpolar pi bond approaches a strongly electron-deficient species (the electrophile) and forms a bond between the electrophile and the atom of the pi bond

Question 20

The product of electrophilic addition is:

Answer 20

a carbocation which is highly unstable and will react further because it has a positive charge and lacks an octet

Question 21

Electrophile elimination happens when

Answer 21

an electrophile (a strongly electron deficient species) is eliminated from the carbocation generating a stable, uncharged organic species

Question 22

carbocations typically appear as

Answer 22

intermediates in multistep mechanisms

Question 23

Carbocations commonly behave as lewis _____

Answer 23

acids to form a bond with an elecron-rich lewis base

Question 24

carbocations can undergo rearrangment ________ it takes part in one of these steps with another species

Answer 24

before

Question 25

2 types of carbocation rearrangements:

Answer 25

hydride shift: a hydride anion is said to shift because a hydrogen atom migrates along with the pair of electrons initially making up the C-H bond

alkyl shift: same except it’s a methyl group, not a hydride

Question 26

Driving force behind a reaction is:

Answer 26

a reflection of the extent to which the reaction favors products over reactants

that tendency increases with increasing stability of the products relative to the reactants

Question 27

Driving force generally increases with:

Answer 27

• greater charge stabilization in the products relative to the reactants
• greater total bond energy in the products relative to the reactants

Question 28

When charge stability and bond energy favor opposite sides of a chemical reaction _______ usually wins:

Answer 28

charge stability

Question 29

Metal cations from group IA of the periodic table behave as ________ and can be _________ when identifying electron-rich sites in an elementary step

Answer 29

spectator ions; disregarded

Question 30

For a reaction or elementary step involving only uncharged species, the side that is favored generally has the greater:

Answer 30

bond energies

Question 31

Electron-poor substrates will have _____________ adjacent to the reactive carbon atoms.

Answer 31

electron-withdrawing leaving groups