41 Questions
What is the result of treating alcohols with a strong acid?
The O is converted into a good leaving group
What type of reaction is dehydration?
An elimination reaction
What is typically required for dehydration to occur?
A strong acid
Which alcohols dehydrate more easily?
More substituted alcohols
What is the mechanism by which 2° and 3° alcohols react?
E1 mechanism
What is the rule that follows the regioselectivity of dehydration?
Zaitsev's rule
What is the product of dehydration when a mixture of constitutional isomers is possible?
The more substituted alkene
What is the role of the amine base in dehydration?
It is present to stabilize the intermediate
What is the primary factor in determining the alkene formed during dehydration?
Removal of the hydrogen from the beta-carbon having the fewest hydrogen substituents
Why cannot 1° alcohols undergo dehydration by an E1 mechanism?
1° carbocations are highly unstable
What is the role of POCl3 in the dehydration of alcohols?
It converts a poor leaving group into a good leaving group
What is the advantage of using POCl3 and pyridine in dehydration reactions?
It allows for dehydration of secondary and tertiary alcohols at low temperatures
What is necessary for a substitution reaction to occur with an alcohol?
The conversion of ¯OH into a good leaving group
What is the result of reacting alcohols with HX (X = Cl, Br, I)?
The formation of alkyl halides
What is the mechanism of dehydration of 1° alcohols?
E2 mechanism
Why is Zaitsev's rule important in dehydration reactions?
It helps to predict the formation of alkenes
What is the typical order of reactivity of alcohols with HX?
More substituted alcohols react more rapidly
Why is ZnCl2 added to the reaction of 1o alcohols with HCl?
To complex with the O atom of the alcohol and facilitate the SN2 reaction
What is the role of SOCl2 in the conversion of alcohols to alkyl halides?
It converts alcohols into alkyl chlorides
What is the purpose of adding a Lewis acid catalyst in the reaction of 1o alcohols with HCl?
To make the O atom of the alcohol a better leaving group
What is the trend in the reactivity of hydrogen halides?
The reactivity increases with increasing acidity
What is the role of PBr3 in the conversion of alcohols to alkyl halides?
It converts alcohols into alkyl bromides
What type of reaction occurs when alcohols react with HX?
SN2 reaction
What is the stereochemistry of the products when the reaction occurs at a stereogenic center?
The stereochemistry can be predicted by knowing the mechanism of the reaction
What is the purpose of SOCl2 and PBr3 in the conversion of alcohols to alkyl halides?
To convert ¯OH into a good leaving group in situ
Why do more substituted alcohols react more rapidly with HX?
Because the reaction mechanism is affected by the structure of the R group
What is the primary function of ZnCl2 in the reaction of 1o alcohols with HCl?
To form a good leaving group
Why do PBr3 and SOCl2 convert alcohols into alkyl halides?
Because they convert ¯OH into a good leaving group and provide a nucleophile
What is the relationship between the acidity of hydrogen halides and their reactivity?
The reactivity of hydrogen halides increases with increasing acidity
What determines the stereochemistry of the products when the reaction occurs at a stereogenic center?
The mechanism of the reaction
What is the role of the R group in the reaction of alcohols with HX?
It determines the mechanism of reaction
Why is Cl¯ a poorer nucleophile than Br¯ or I¯?
Because it is a smaller atom
What is the difference between the reaction of 1o alcohols with HCl and 2o or 3o alcohols with HX?
The reaction of 1o alcohols requires a catalyst, while 2o or 3o alcohols do not
What is the function of the Lewis acid catalyst in the reaction of 1o alcohols with HCl?
To complex with the O atom of the alcohol
Why do more substituted alcohols react more rapidly with HX?
Because they have a more stable carbocation intermediate
What is the purpose of using thionyl chloride and phosphorus tribromide in the conversion of alcohols to alkyl halides?
To convert ¯OH into a good leaving group and provide a nucleophile
More substituted alcohols react less rapidly with HX
False
The reaction of 1o alcohols with HCl occurs without an additional Lewis acid catalyst
False
SOCl2 converts alcohols into alkyl bromides
False
The acidity of hydrogen halides decreases with increasing reactivity
False
Complexation of ZnCl2 with the O atom of the alcohol makes a poor leaving group
False
Test your understanding of alcohols in organic chemistry, including substitution and elimination reactions. Learn how treatment with a strong acid enables these reactions and how dehydration occurs. Evaluate your knowledge of the mechanisms and products of these reactions.
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