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Ochem 353 > Alkenes + Alkynes > Flashcards

Alkenes + Alkynes Flashcards

1
Q

What does dehydration of ROH lead to

A

Double bonds

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2
Q

What is the alpha carbon

What about beta

A

First Carbon attached to the functional group

Beta is the carbon next to the alpha carbon

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3
Q

What are common H+ catalysts

A

H2SO4, H3PO4, KHSO4

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4
Q

Under acidic conditions what type of catalyst do you want

Under basic?

A

Want cations or neutral

Want anions or neutral

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5
Q

When doing dehydration reactions (remove oh and make double bond) what are the conditions needed for primary to tertiary ROH

A

Primary neeeds higher temp/nrg, has higher transition state

Going to tertiary you need lower temp/nrg, lower transition state

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6
Q

When does Zaitsevs rule happen?

What type of reaction is it

A

When you have inequivalent beta carbon, have to choose where double bond goes

Regioselective reaction

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7
Q

What is sterioselectivity

A

Antizaitsev product can give either cos or trans isomer

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8
Q

What is regiospecific

A

Want more electron donating (methyl groups) in the product

Results in only one product

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9
Q

Beta elimination reactions of ROH’s use what and give what as the product

A

Use H2SO4 of remove OH and make double bond

Give most highly substituted Alkene as the product and can make cos and trans isomers of the product

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10
Q

What products are more stable in beta elimination reaction

A

The trans (E) Isomer

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11
Q

What compunds are good for alcohol dehydration
(E2)

A

H3PO4
H2SO4
KHSO4

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12
Q

Where are 1,2 hydride shifts common

A

In primary roh (oh on primary carbon)

Concerted (E2)

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13
Q

F is a ___

A

Bad LG

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14
Q

What are examples of small bases

What do they give

A

NaOme

KOH

EtOH

Zairsev product

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15
Q

If you have a primary alkyl halide and want a terminal Alkene (want antizaitsev) what do you use

A

Ktbu/heat and DMSO

bulky base, aprotic solvent

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16
Q

Electron donating groups do what to a double bond

A

Stabilize it, this is why zaitsev is best

17
Q

Do hydride shifts occur under basic conditions

A

No

18
Q

Is ring systems where cos and trans is possible, which conformation about the double bond it better

A

Cis because less steric hindrance

(Slide 16)

19
Q

What is a double dehydrohalogenation

A

Two halogens on compound, removing both to make a triple bond

20
Q

What is a geminal dihalide

What is vicinal dihalide

A

The halogens cl,br,I are connected to the same carbon

The halogens are connected to different carbons

21
Q

What do you need to go from a geminal dihalide to an alkyne

A
  1. 3 equiv of NaNH2, in liq. NH3
  2. H2O
22
Q

Why is the pka of a terminal alkyne lower (25)

A

The s charcter is increased so if h was taken of of it the anion would be stabilized since it’s close to the nucleus

It would be deprotonated in geminal di halide reactions

Then become excellent nucleophile

23
Q

What is the basic concept in addition reactions

A

Have Nu—E with c=c. Then double bond is gone and NU and E are added

24
Q

What is the basic steps in addition reactions

A
  1. Transformation
  2. Regiochemistry
  3. Stereochemistry
25
Q

What does the transformation step in addition reactions tell us

A

What functional groups to install

This tells us what E and NU need to be

26
Q

What does the regiochemistry step in addition reactions tell us

A

When the E+ add first, it determines the regiochem

27
Q

What does the stereochemistry step in addition reactions tell us

A

If there’s a carbocation involved it’s not stereoselective (something can come from top to bottom equally)

If the new sigma binds from concerted it’s syn addition (E AND NU added to same side

If the new signs binds form stepwise it’s anti addition

28
Q

What is used in hydrogenation of alkynes

A

H2/metal catalyst like Pf,Pt,Ni,Rh

It’s a two phase reaction that always end with alkane because

The alkyne towline step happens faster because the pi bind is weaker

Always does syn addition

29
Q

What is lindlars catalyst

A

A catalyst used with h2 to just make alkyne to cis Alkene

It’s doesn’t go to alkane because it’s a WEAK catalyst

30
Q

What determines if it’s syn addition to the top part of a complex ring or bottom part

A

If there’s too much crowding on one side, the H won’t be added to that side

31
Q

To go from alkyne to Alkene you need

A

2 equiv of H2 and one metal catalyst

32
Q

Does a terminal or internal alkyne have the largest fall in energy to Alkene

A

Terminal because more s character

Ochem 353 (2 decks)

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