04/30/2024

Question 1

What is halogenation and what are its features

Answer 1

it is the addition of a halogen (typically Br2 or Cl2) to an alkene.

It follows an anti addition and a cyclicbromonium ion formation

it has a similar mechanism to an SN2 reaction where the bromide ion attacks the cyclicbromonium ion from the back

Question 2

What is a halohydrogenation and what are the features

Answer 2

it is an anti addition oh Br2 in an H20 solvent

rather than the bromide acting as nucleophile, the h20 is in abundance and acts as a nucleophile to add a h20 to the backside of the cyclicbromonium ion

Question 3

in a hydrohalogenation, what is acting as a nucleophile

Answer 3

the h20 is in abundance and will preform the backside attack rather than the Br- anion

Question 4

is a cyclicbromonium ion stable or unstable? why?

Answer 4

it is unstable because it is a 3 membered ring, it wants to open so it is reactive

Question 5

what is a syn addition

Answer 5

it is addition to the same side

Question 6

what is anti addition

Answer 6

it is an addition to opposite sides

Question 7

where does the OH add to on a halohydrin reaction?

Answer 7

it adds to the more substituted carbon (most carbonation-like character)

Question 8

what are some intermediates

Answer 8

carbocations, carbanions, radical, carbenes

Question 9

why are reactive intermediates important

Answer 9

they make reactions happen

Question 10

what are carbenes used for

Answer 10

to make cyclopropanes

Question 11

why are cyclopropanes unstable

Answer 11

they have an angle strain (60 degrees deviation from 109.5)

torsional strain with eclipsing hydrogens

Question 12

what is the charge of a carbene

Answer 12

it has no charge, it is neutral

Question 13

what is a stereospecific reaction

Answer 13

it is the retention of stereochemistry

if your starting material is trans, your ending product is trans

if your starting material is cis, your ending material is cis

Question 14

when we use :CH2 in a reaction, what forms and what is a stereochemical feature about it?

Answer 14

it forms a cyclopropane

it has stereoselectivity where the stereochemistry of the alkene is retained in the cyclopropane

Question 15

what does it mean to be divalent and what is an example of it?

Answer 15

divalent means two bonds, carbenes are divalent, they have two bonds

Question 16

how many valence electrons does a carbene have? why is this important

Answer 16

carbenes have 6 valence electrons

carbons want 8 electrons, so carbenes are highly reactive

Question 17

what is special about carbenes? do they act as nucleophiles or electrophiles

Answer 17

they can act as both, they are deficient in electrons (6) and can receive electrons, which gives it an electrophilic character

but it can also donate electrons due to the lone pair on the carbon, this gives it a nucleophilic character

Question 18

explain how alkenes and carbenes interact

Answer 18

since carbenes are electron deficient, they receive electron density from the electron rich region of the pi bond

since carbenes have a lone pair, they can donate electrons to the pi bond and act as a nucleophile

this forms two bonds at the same time, which is why stereospecificity occurs

Question 19

why are carbenes stereospecific

Answer 19

they donate and accept electrons in a concerted mechanism, which gives no opportunity for free rotation and retains stereochemistry

Question 20

will you ever get a mix of cis and trans when using carbenes

Answer 20

no

Question 21

how can we use carbenes? what needs to happen first?

Answer 21

carbenes need to be generated “in situ” and then must be reacted with something else quickly

Question 22

what does it mean to be generated “In-Situ”

Answer 22

it means it is made during the reaction

Question 23

how is diazomethane used to make carbenes

Answer 23

diazomethane when activated with heat or light breaks its C-N bond to form a carbene “in situ” and nitrogen gas (favorable and stable)

Question 24

if you use hydroxide and CHCl3 on an alkene what will form

Answer 24

a cyclopropane with a geminal dihalide

Question 25

what is the function of OH and CHBr3, CHI3, CHCl3?

Answer 25

bromoform, iodoform, and chloroform are used to create a carbene that can create a cyclopropane with a gem-dihalide

Question 26

what is the effect of the three chlorides on the carbon in chloroform?

Answer 26

they pull electron density away from the carbon, which makes the C-H more easily broken

Question 27

what is the pka of chloroform

Answer 27

24

Question 28

what is the process of using OH/CHCl3 with an alkene

Answer 28

first the OH deprotonates CHCl3 in an alpha elimination
Then the Chloride leaves and forms a carbene :CCl2

Question 29

what is a simmons smith reaction

Answer 29

it creates a cyclopropane through a carbenoid

Question 30

what is a carbenoid

Answer 30

a carbenoid is something that is “Carbon-like” where it acts like a carbene but doesn’t actually form one

its good to use when we don’t want gas or dihalides, it is generally safer

Question 31

What is involved in Simmons Smith

Answer 31

CH2I2 + Zn(Cu)

Question 32

draw a spirocyclic compound

Answer 32

its in your notes