Please help with the following problem.
Which of the two reactions proceed faster:
a.) CH3CH2I in presence of ethanol
b.) CH3CH2I in presence of dimethyl sulfoxide© BrainMass Inc. brainmass.com October 16, 2018, 3:37 pm ad1c9bdddf
The reaction is a SN2 reaction.
For an SN2 reaction, the effect of solvent polarity is usually much less, but the ability (or really lack there of) of the solvent to solvate the nucleophile is the important criteria.
The solvent used in a substitution reaction will influence which pathway will be chosen. There are three major categories of solvent.
Polar Protic Solvents
Polar Aprotic Solvents
Non-Polar Aprotic ...
The following posting helps with a problem involving organic reaction intermediates and mechanisms. The concepts covered in the solution include SN2 reactions, solvent polarity and nucleophiles. Detailed explanations are given.
Aldol Reactions : Trans-4-Nitrochalcone
8.88) In a number of cases it is possible to successfully isolate the B-Hydroxyketone intermediate prior to the dehydration that froms the alpha,Beta unsaturated ketone.
(a) Does the isolation of the B-Hydroxyketone suggest which step in the aldol condesnation is the rate determining step in this case?
(b)if so, Which one is the rate determining step?
(c)Suggest what reaction conditions may have a significant impact on determing which step becomes rate determining.
(d)What Structural changes might lead to a change in the rate determing step?
8.89) KEtones also undergo the aldo condensation, although a succesful reaction often requires "enhanced" conditions, since the addition involves an unfavorable equilibrium constant. This situation in the reaction in which 4 nitrochalcone is synthesized. With odds against it, why i the rreaction successful in this case?
8-92) Give the aldol product or products from the following reaction:
CH3CH2CH2CH2CH2CHO + CH3CH2CH2CH2CHO --base->
8.94) The mixed aldol reaction between propionaldehyde and acetne gives an 85% yield if 4 hydroxy - 2- hexanone when run in THF at -78 degrees C with lithium diisopropylamide (LDA, a powerful base). The reaction is carried out by first adding the ketone to the base, cooling the solution , and then adding the aldehyde.
(a) Why does this muxed system give essentially a single product?
(b) Why is there noself condensation of the acetone?
(c) Why does the system not rapidly go on to dehydrate?
(d) Why is the keyone added to the base rather than Vice-versa?
8.96) If you had obtained both the cis- and trans-chalcone products, adn had purified them by recrystallization, how could you instantly know which one was cis and which one was trans without any further characterization?View Full Posting Details