Org 1 Review - Reactions of Alkenes

Section 1

Question	Answer
What's Markovnikoff's rule?	Markovnikoff's rule: in the addition of hydrogen halides to alkenes, the nucleophile attaches to the most substituted carbon
What's the order of carbocation stability for primary, secondary, and tertiary carbocations?	tertiary carbocation is most stable followed by secondary then primary
What's the difference between "dehydration" and "dehydrogenation"	Dehydration is loss of water (H2O). Dehydrogenation is loss of H2.
The stability of carbocations increases as the number of carbons attached to the carbon [increases/decreases]	Increases
The name for the phenomenon where adjacent p-orbitals line up and delocalize their bonding is called _____.	conjugation
A reaction that produces 2-butanol from butene selectively would be called _____selective.	regioselective
The reaction of 1-butene with HBr produces 2-bromobutane. Is this an enantioselective reaction? Why/why not?	Not an enantioselective reaction - it goes through a carbocation, which flat, has a mirror plane and is thus achiral.
True or false: when you do a hydroboration reaction on a molecule that already has a chiral center, you will form a mixture of enantiomers.	False - you will make a mixture of diastereomers. This is because you already have a chiral center, and your reaction will not invert this - so there's no way you can make a mixture of enantiomers.
What is the regioselectivity of the hydroboration reaction?	The regioselectivity of the hydroboration reaction is anti-Markovnikoff (the boron adds to the less substituted end of the double bond)
What is the stereochemistry of the hydroboration reaction?	The stereochemistry of the hydroboration reaction is "syn".
	memorize

Section 2

Question	Answer
What reaction would you use to produce 1-butanol from 1-butene?	Use hydroboration for this reaction, as you want the alcohol on the less substituted end of the double bond.
What is the stereochemistry of the bromination reaction (using Br-Br)?	It's trans - you form a 3-membered ring, and attack onto this gives trans.
What's the stereochemistry of additions of hydrogen halides to alkenes?	The stereochemistry is random - you go through a free carbocation, so there is no preferred stereochemistry - nucleophile can attack from either face.
The addition of one molecule of H2 to a double bond is called ________. It requires a catalyst in order to occur. The stereochemistry of hydrogenation reactions is ____.	Addition of H2 is called hydrogenation. Stereochemistry is "syn".
What are the two key steps in the bromination of an alkene with Br2?	The first step is formation of the 3 membered ring (bromonium ion). The second step is attack of the Br(-) anion to the backside of the most substituted carbon of the bridge, resulting in a trans dibromide.
How do the products of the bromination reaction change if you use water as a solvent?	If you use water as solvent, you get attack of the solvent on the bromonium ion instead of Br(–) - (the molecule is reactive and surrounded by the nucleophilic water molecules). The product will have an OH. this is called a halohydrin.
What is formed when you treat an alkene with a per-acid, RC(O)OOH [the O in brackets is a carbonyl, C=O] ?	Form an epoxide (oxirane)
When HCl is added to 1-propene, the product is 2-chloropropane. Outline the two main steps in this reaction.	Two main steps: the pi bond (double bond) attacks H+, which produces a carbocation. The more substituted carbocation will be produced selectively since it is most stable. Then the carbocation is quenched by reaction with the Cl(-), to give 2-chloropropene.
What is the purpose of H2O2 in the hydroboration reaction?	purpose of H2O2 is to oxidize the C-B bond to a C-O bond when the reaction is complete. This is what allows for the formation of alcohols.
What is meant by the "more substituted" end of a double bond.	by "more substituted end of double bond" it is generally meant, "the end of the double bond with fewest hydrogens (or most carbons)"
True or false - any time you go through a carbocation (or a free radical) the reaction will be stereorandom.	True
Let's say you start with 1-butene. If you needed to make 1-butanol, what conditions would you use? If you had to make 2-butanol, what conditions could you use?	To make 1-butanol you need anti-Markovnikoff addition, so you'd use BH3 and H2O2. To make 2-butanol you'd need Markovnikoff addition and thus use either H3O(+) or HgX2 plus water followed by NaBH4.
In the bromination of cyclohexene with Br2, you will form two stereoisomers. What will be the relationship of those two stereoisomers? Why do you get a mixture of the two?	The two stereoisomers will be enantiomers. This happens because you will form 50% of the bromonium ions on the top face of the alkene and 50% on the bottom face, and subsequent attack will give you the two enantiomers.
	memorize

 

Org 1 Review - Thermodynamics
Org 1 Review - Free Radicals
Org 1 Review - Reactions of Alcohols
Org 1 Review - Alkynes
Org 1 Review - Substitution and Elimination
Org 1 Review - Reactions of Double Bonds
Org 1 Review - Stereochemistry
Org 1 Review - Conformations
Org 1 Review - Structure and Bonding

Section 3