Ochem5 Alkenes

Question 1

What is the general formula for straight chain alkenes with one double bond?

Answer 1

CnH2n

Question 2

What is the formula for the degree of unsaturation, using the formula CnHm?

Answer 2

N (unsaturation) = 1/2 (2n+2-m)

Question 3

What is another name for alkenes?

Answer 3

Olefins

Question 4

As molecular weight of alkenes increases, how are bp and mp affected?

Which boil at a higher temp, terminal or internal alkenes?

Which have higher bps, trans or cis alkenes?

Answer 4

Increase

Internal alkenes

Cis -more polar than trans

Question 5

Which molecules are more polar, trans or cis molecules?

So which has a higher bp?

Which has a higher melting point?

Answer 5

Cis, dipoles point in the same direction

For trans they point in opposite directions and cancel each other out.

Cis have a higher bp because higher polarity means more intermolecular forces

Trans - more symmetry means tighter packing

Question 6

The reaction that forms of an alkene from a halide or an alcohol

Answer 6

Elimination Reaction

Question 7

This type of elimination reaction is a two step process proceeding through a carbocation intermediate. The rate is dependent upon only one species

Answer 7

E1

Question 8

What conditions favor E1?

Answer 8

Same as Sn1

Polar solvents, highly branched chains, good leaving groups, weak nucleophiles in low concentration.

Directing a reaction towards Sn1 or E1 alone is difficult so they usually occur together

Question 9

This type of elimination reaction occurs in one step, and its rate is dependent upon two species

Answer 9

E2

Question 10

There are often multiple products in E2 reactions, what product is usually more favored?

Answer 10

The more substituted double bond

Question 11

Does steric hinderance affect E2 reactions?

So do highly substituted carbon chains favor Sn2 or E2?

Answer 11

No.

E2, rarely Sn2

Question 12

Strong nucleophiles and weak bases favor which reaction, Sn1, Sn2, E2, E1

What are some examples of strong nucleophiles but weak bases?

Answer 12

Sn2

CN-, N3-, Cl-, Br-, I-, SH-, SR-

Question 13

Strong bases but weak nucleophiles favor which reaction, Sn1, Sn2, E2, E1?

What are some examples of strong bases but weak nucleophiles?

Answer 13

E2

Large sterically hindered compounds with negative charges on Oxygen, etc.

Question 14

For which reaction is rearrangement possible?

Answer 14

E1

Question 15

For which reaction must there be anticoplanar stereochemistry?

Answer 15

E2`

Question 16

What are some examples of molecules that are strong nucleophiles and strong bases?

If the compound its reacting with is primary, which reaction does it favor?

Tertiary?

Secondary?

Answer 16

OH-, -OCH3, -OCH2CH3

Sn2

E2

Either, depends upon other conditions

Question 17

Which reaction favors a weak base?

and a weak nucleophile?

What are examples of these compounds?

Answer 17

E1

Sn1

CH3CH2OH