Chapter 7

Question 1

Alkyl Halides:

Answer 1

Organic Molecules containing a halogen atom (X) bonded to an sp^3 hybridized carbon atom

Question 2

Alkyl Halides are classified as:

Answer 2

-Primary
-Secondary
-Tertiary
This is dependent on the number of carbons bonded to the carbon with the halogen

Question 3

What is the most important factor in determining the course of an alkyl halides chemical reactions?

Answer 3

The classification

Question 4

What is the general molecular formula of alkyl halides?

Answer 4

Cn H2n+1 X

Question 5

Where are alkyl halides formally derived from?

Answer 5

Replacing a hydrogen atom with a halogen

Question 6

What are the 4 types of organic halides?

Answer 6

• Vinyl Halides
• Aryl Halides
• Allylic Halid
• Benzylic Halide

Question 7

Vinyl Halides:

Answer 7

Have a halogen atom bonded to a carbon-carbon double bond

Question 8

Aryl Halides:

Answer 8

Have a halogen atom bonded to a benzene ring

Question 9

Which two halides do not undergo the reactions in this chapter?

Answer 9

Vinyl and Aryl halides.

These are also attached to an sp2 hybridized C

Question 10

Which halides undergo the reactions in this chapter?

Answer 10

Allylic and Benzylic halides

These are also bonded to an sp3 hybridized carbon

Question 11

Allylic Halides:

Answer 11

Have X bonded to the carbon atom adjacent to a carbon carbon double bond

Question 12

Benzylic Halides:

Answer 12

Have X Bonded to the carbon atom adjacent to a benzene ring

Question 13

Fun Fact:

Answer 13

Hundreds of organic halides with diverse structures and biological activities have been isolate from red algae of the genus Laurencia, seaweed that grows in shallow water at the edges of reefs

Question 14

Name properties of alkyl halides:

Answer 14

• weakly polar molecules
• soluble in organic solvents
• not water soluble
• exhibit dipole-dipole interactions
• As the C chain grows longer, it overshadows the weakly-polar C-X bond, making the molecule less polar

Question 15

Alkyl halides undergo nucleophilic substitution reactions. Select all components that are required for a nucleophilic substitution reaction to take place.

Answer 15

• a leaving group
• a nucleophile
• an sp3 hybridized C bonded to the leaving group

Question 16

What is the chemical formula for carbon tetrachloride?

Answer 16

CCl4

Question 17

What is the chemical formula for Chloroform?

Answer 17

CHCl3

Question 18

What is the chemical formula for dichloromethane?

Answer 18

CH2Cl2

Question 19

Describe the nucleophilic substitution of an alkyl halide:

Answer 19

• a nucleophile donates an electron pair to an electrophilic C atom
• As the C-X bond is cleaved, the electrons of the C-X sigma bond are accepted by the leaving group
• The C-X bond is cleaved heterolytically to form radicals
• The reaction takes place at an sp3 hybridized C atom

Question 20

In any nucleophilic reaction a ________ attacks an ____ hybridized C atom and displaces a ______ group

Answer 20

nucleo
sp3
leaving

Question 21

T/F Negatively charged nucleophiles are often used as salts. The identity of the counterion used to balance the charge is often inconsequential, and therefore it is omitted from the chemical equation.

Answer 21

True

Reason: Nucleophiles like -SH are often used as salts with Li+, Na+, or K+ counterions.

Question 22

The following steps are needed to draw the product of any nucleophilic substitution reaction. Place the steps in the correct order with the first step at the top of the list.

Answer 22

1. Find the sp3 hybridized carbon with the leaving group
2. Identify the nucleophile, the species with a lone pair or pi bond
3. Substitute the nucleophile for the leaving group and assign charges (if necessary) to any atom involved in bond breaking/formation

Question 23

The nucleophile ____ an electron pair

Answer 23

donates

Question 24

The carbon atom at which substitution occurs ____ an electron pair from the nucleophile

Answer 24

accepts

Question 25

The lewis base in a nucleophilic substitution reaction is the

Answer 25

nucleophile

Question 26

The lewis in a nucleophilic substitution reaction is the _______

Answer 26

carbon atom at which substitution occurs

Question 27

All good leaving groups are ____ bases with relatively ____ conjugate acids that have _____ pKa values

Answer 27

weaker strong low

Question 28

Leaving group ability _____ from left to right across a row of the periodic tables as basicity ______

Answer 28

increases | decreases

Question 29

Is Cl- a good leaving group?

Answer 29

Yes, it is a weak base

Question 30

Rate I- , H2N-, HO-, and Br- from best to worst leaving group

Answer 30

I- Br- HO- H2N-

Question 31

Why is F- a poor leaving group?

Answer 31

The C-F bond is very strong

Question 32

Is H2O a good leaving group?

Answer 32

Yes because it is a weak base

Question 33

Is HO- a good leaving group?

Answer 33

No it is a strong base and a poor leaving group

Question 34

Is I- a good leaving group?

Answer 34

Yes it is a weak base

Question 35

What is steric hindrance?

Answer 35

A decrease in reactivity resulting from the presence of bulky groups at the site of a reaction

Question 36

Nucleophilicity does not parallel basicity when ____ ______ becomes important

Answer 36

Steric Hindrance

Question 37

What is steric strain?

Answer 37

An increase in energy when big groups (occupying a large volume) are forced close to each other

Question 38

The steric bulk of the tert-butoxide anion ______ its reactivity as a nucleophile without affecting its ability to act as a base. A sterically hindered based that is a poor nucleophile is called a _________ base

Answer 38

decreases; | nonnucleophilic

Question 39

What are comparisons between nucleophiles and bases?

Answer 39

- A nucleophile is a lewis base that attacks electrophiles other than protons - Nucleophiles and bases have a lone pair or pi bond

Question 40

It is generally true that a strong base is a ______ nucleophile, although steric factors and solvent effects can alter this relationship

Answer 40

strong

Question 41

Are polar protic solvents capable of intermolecular hydrogen ponding? And why?

Answer 41

Yes because they contain an O-H or N-H bond.

Question 42

Do polar protic solvents solvate cations are anions?

Answer 42

They solvate both well.

Question 43

Cations are solvated by?

Answer 43

Ion-dipole interactions

Question 44

Anions are solvated by?

Answer 44

Hydrogen bonding

Question 45

Nucleophilicity increases _____ a column of the periodic table

Answer 45

down

Question 46

In a polar protic solvent, nucleophilicity _____ down a group of the periodic table as the size of the anion _____ and basicity _____.

Answer 46

increases increases decreases

Question 47

What are correct characteristics of polar aprotic solvents?

Answer 47

- A polar aprotic solvent solvates cations by ion-dipole interactions. - Acetone is a polar aprotic solvent because it cannot act as a hydrogen-bond donor

Question 48

Which solvents are both polar and protic?

Answer 48

- water, H2O - acetic acid, CH3COOH - ethanol, CH3CH2OH

Question 49

T/F HS- is a more powerful nucleophile than HO-

Answer 49

True

Question 50

T/F smaller anions are more strongly solvated than large anions and are less nucleophilic.

Answer 50

True

Question 51

T/F Nucleophilicity increases up a column of the periodic table

Answer 51

False. Nucleophilicity increases down a column of the periodic table

Question 52

In a polar aprotic solvent such as acetone, the _____ the base the stronger the nucleophile. In this type of solvent, nucleophilicity ______ down a group on the periodic table as basicity ______

Answer 52

stronger decreases decreases

Question 53

In a polar aprotic solvent such as acetone, Cl– is a _____ nucleophile than Br– but in a polar protic solvent Cl– is the _____ nucleophile of the pair.

Answer 53

stronger | weaker

Question 54

SN2 reactions _____.

Answer 54

- are bimolecular reactions | - follow second order kinetics

Question 55

The hydroxide anion –OH is a _____ base than the chloride anion Cl– and therefore in a polar aprotic solvent –OH will be a _____ nucleophile.

Answer 55

stronger | stronger

Question 56

What does backside attack allow?

Answer 56

The reacting carbon to retain its stereochemistry

Question 57

Select all the statements that describe the mechanism of the SN2 reaction.

Answer 57

- the bond to the nucleophile is formed in the same step as the bond to the leaving group is broken - the reaction follows second-order kinetics - complete inversion of stereochemistry is observed at the reacting center

Question 58

Sn1 reaction:

Answer 58

The rate is doubled when the concentration of the alkyl halide is doubled.

Question 59

sn2 reaction:

Answer 59

The rate is quadrupled when the concentration of both the alkyl halide and nucleophile are doubled.

Question 60

Select all the statements that correctly describe the reaction coordinate vs. energy diagram for an SN1 reaction.

Answer 60

The energy diagram shows two energy maxima corresponding to the two transition states. The first step of the reaction is endothermic. The energy of the first transition state is higher than the energy of the second transition state.

Question 61

As the degree of substitution of an alkyl halide increases, the rate of the SN2 reaction it undergoes will _____. A 1° alkyl halide will therefore have a _____ rate of reaction than a 2° alkyl halide.

Answer 61

decrease | faster

Question 62

Describe the structure of a carbocation.

Answer 62

The positively charged C atom of a carbocation has an empty p orbital available for bonding. The positively charged C atom of a carbocation is sp2 hybridized.

Question 63

An SN1 reaction is a _____-step process whose energy diagram contains _____ transition state(s) and _____ reactive intermediate(s).t

Answer 63

two two one

Question 64

Racemization is the formation of equal amounts of two products that are _______ of each other from a single chiral starting material

Answer 64

enantiomers

Question 65

Which type of alkyl halide is most reactive in an SN1 reaction?

Answer 65

Tertiary

Question 66

Correctly describe inductive effects:

Answer 66

Inductive effects operate through σ bonds only. Alkyl groups can stabilize a positive charge by induction.

Question 67

The Hammond postulate does what:

Answer 67

The rate of a reaction depends on Ea, and the stability of a product depends on ΔG°. The Hammond postulate provides an estimate of the energy of the transition state for a reaction.