GRE Subject Test: Chemistry : Alkene Chemistry
Study concepts, example questions & explanations for GRE Subject Test: Chemistry
All GRE Subject Test: Chemistry Resources
Example Questions
Example Question #1 :Reactions By Product
What is the IUPAC name of the given diene?
3-chloro-2,5-dimethyl-1,5-heptadiene
3-chloro-2,5-dimethyl-2,6-heptadiene
5-chloro-3,5-dimethyl-1,6-heptadiene
None of these answers
5-chloro-3,6-dimethyl-1,5-heptadiene
5-chloro-3,6-dimethyl-1,5-heptadiene
You must begin counting the carbons so that the first functional substituent has the lowest possible number. In this case, C1 is connected to C2 by the double bond, meaning we start counting from the left.
The longest carbon chain is seven carbons so the parent molecule is heptane. With this numbering, there are methyl groups on carbons 3 and 6 and a chlorine on carbon 5.
Substituents are named in alphabetical order and two double bonds result in a diene. Thus, the correct answer is 5-chloro-3,6-dimethyl-1,5-heptadiene.
Example Question #1 :Reactions By Reactant
The stereochemical pathway for the hydrogenation of an alkene with a metal catalyst, such as platinum, occurs via__________.
Markovnikov addition
syn addition
anti-Markovnikov addition
anti addition
formation of a bridged carbocation
syn addition
Hydrogenation of an alkene with a metal catalyst, such as platinum, occurs via syn addition.
It is important to note the three main types of reactions for alkenes. The first type of reaction is a 2-step mechanism in which the electrophile attacks the carbocation nucleophile. This can yield syn or anti products. The second type of reaction is a 2-step mechanism that forms a bridged carbocation as the intermediate. This can yield only anti products. The third and last type of reaction is a 1-step addition. This can only yield syn products.
An example of the third type of reaction is the addition of a hydrogen with palladium, platinum, or nickel as demonstrated in the picture.
Example Question #1 :Hydrocarbons
What is(are) the product(s) in the Pd-catalyzed hydrogenation if 1,2-dimethylcyclopentene?
Dimethylcyclopentane
Cis-1,2-dimethylcyclopentane
1,1-dimethylcyclopentene
Trans-1,2-dimethylcyclopentane
A mixture oftrans-andcis-1,2-dimethylcyclopentane
Cis-1,2-dimethylcyclopentane
该加氢的产品cis-1,2-dimethylcyclopentane.
It is important to note the three main types of reactions for alkenes. The first type of reaction is a 2-step mechanism in which the electrophile attacks the carbocation nucleophile. This can yield syn or anti products. The second type of reaction is a 2-step mechanism that forms a bridged carbocation as the intermediate. This can yield only anti products. The third and last type of reaction is a 1-step addition. This can only yield syn products.
Thecisproduct alone forms because the reagents used were hydrogen and a metal catalyst palladium (other common metal catalysts are platinum and nickel). This type of reagent with an alkene will always be a 1-step addition that yields solelysynproducts.Cis-1,2-dimethylcyclopentane is the only answer that solely indicatessynproducts.
Example Question #1 :Help With Alkene Reactions
What reagent will complete this reaction?
N-bromosuccinimide (NBS) / light
SOBr2
Br2/ light
None of these
PBr3
N-bromosuccinimide (NBS) / light
N-bromosuccinimide (NBS) brominates at allylic positions. Br2will not complete this reaction with the presence of the double bond.
Certified Tutor
Certified Tutor
All GRE Subject Test: Chemistry Resources
