Chapter 7

Question 1

alkyne

Answer 1

an unsaturated hydrocarbon that contains one or more carbon-carbon triple bonds

Question 2

IUPAC

Answer 2

1. parent chain: longest carbon chain containing the alkyne
2. number the carbon chain giving the lowest number to the first multiple bond (DB beats TP)
3. -infix- = “yn”

Question 3

physical properties of alkynes

Answer 3

• only attractive forces between alkynes are dispersion forces
• colorless
• nonpolar
• insoluble in water
• less dense than water

Question 4

acidity

Answer 4

sp hybridization leads to increased acidity of terminal alkynes (pka~25) relative to alkenes (sp2; pka ~44) and alkanes (sp3; pKa~51)
-alkanes > alkenes > alkynes

Question 5

strong bases capable of deprotonating terminal alkynes

Answer 5

• Hydride: “Hard” base (100% s character, very EN), decreases chance of it “attacking” atoms, and deprotonates instead
• Lithium disopropyl amide (LDA): “Bulky” base, decreases chance of it “attacking” atoms, and deprotonates instead

Question 6

Preparation of Alkynes

Answer 6

A. alkylation of acetylide anions with primary haloalkanes

B. Alkynes from Alkenes (dehydrohalogenation reaction)

Question 7

alkylation reaction

Answer 7

any reaction in which a new carbon-carbon bond to an alkyl group is formed

Question 8

dehydrohalogenation reaction

Answer 8

removal of -H and -X from adjacent carbons

Question 9

addition of bromine and chlorine to Alkyne

Answer 9

stereoselective: during the first addition -Br adds from the opposite face of the triple bond (anti stereoselective), yielding a trans isomer. The second addition removes stereo centers

Question 10

addition of hydrogen halides

Answer 10

regioselective: maokovnikov addition (halogen goes onto the more substituted carbon for both additions)

Question 11

hydroboration-oxidation

Answer 11

bulky boron is used to prevent multiple hydroborations, which occurs for terminal alkynes with BH3, but not internal alkynes

• keto-enol tautomerism
• regioselective: non-Markovnikov addition (-H goes onto the carbon with fewer hydrogens)
• stereoselective: in the first step hydrogen and boron add from the same face of the triple bond, but the final products do not contain new stereocenters

Question 12

enol

Answer 12

a compound containing a hydroxyl group bonded to a C=C double bond

Question 13

tautomers

Answer 13

constitutional isomers in equilibrium with each other that differ in the location of a hydrogen atom and a double bond relative to a heteroatom

Question 14

keto-enol tautomerism

Answer 14

a type of isomerism involving keto (from ketone) and Enol tautomers

Question 15

acid-catalyzed hydration

Answer 15

regioselective: Markovnikov addition (-H goes onto the carbon with more hydrogens)
stereoselective: In the first step water and Hg add from the opposite face of the triple bond but the final products do not contain new stereocenters

Question 16

catalytic reduction

Answer 16

• lindlar catalyst

- stereoselective: both hydrogens add from the same face of the triple bond

Question 17

lindlar catalyst

Answer 17

Pd-based catalyst that reduces alkynes to cis alkenes

Question 18

hydrobration-protonolysis

Answer 18

-stereoselective: in the first step hydrogen and boron add from the same face of the triple bond and maintain that configuration upon protonolysis and a carboxylic acid

Question 19

protonolysis

Answer 19

cleavage of a chemical bond by acid

Question 20

dissolving-metal reaction

Answer 20

stereoselective: hydrogens add from the opposite face of the triple bond and yield a trans double bond

Question 21

organic synthesis

Answer 21

a series of reactions by which a set of organic starting materials are converted to a more complicated structure
*functional groups often react in the same fashion, whether in a simple or complex molecule

Question 22

retrosynthetic analysis

Answer 22

working backward from the desired product in order to plan a synthesis

target molecule => starting materials

analyze the target molecule in the following ways:

1. carbon skeleton: how can we put it together? only way to make a C-C bond is alkylation with alkyne anions
2. functional groups: what are they, how can be transformed, and how can the choice of reagents provide the exact target?