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Tautomerization quiz #1

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  • What occurs during a tautomeric shift in ketones or aldehydes, and what are the resulting tautomers called?
    During a tautomeric shift in ketones or aldehydes, the location of a pi bond and a hydrogen atom are switched, resulting in the formation of constitutional isomers called tautomers. The two main tautomers are the keto tautomer (which resembles the original carbonyl structure) and the enol tautomer (which features a vinyl alcohol, with an alcohol group directly attached to a double bond).
  • What is the pKa of a typical alkane compared to an alpha carbon adjacent to a carbonyl group?
    A typical alkane has a pKa of about 50, while an alpha carbon next to a carbonyl has a pKa of about 20. This means the alpha carbon is much more acidic than a regular alkane.
  • Why are alpha carbons significantly more acidic than regular alkanes?
    Alpha carbons are more acidic because tautomerization allows the formation of a stable conjugate base or molecule after deprotonation. This stability is not present in regular alkanes.
  • What happens to the location of a pi bond and a hydrogen atom during tautomerization?
    During tautomerization, the pi bond and a hydrogen atom switch places within the molecule. This results in the formation of constitutional isomers called tautomers.
  • What is the main difference between resonance structures and tautomers?
    Resonance structures involve the movement of electrons only, while tautomers involve the movement of atoms, specifically hydrogen and the pi bond. Tautomers are constitutional isomers, not resonance forms.
  • In acid-catalyzed tautomerization, what is the first step of the mechanism?
    The first step in acid-catalyzed tautomerization is protonation of the carbonyl oxygen. This creates a positively charged carbonyl intermediate.
  • What intermediate is formed during base-catalyzed tautomerization before the enol is produced?
    A negatively charged enolate ion is formed as an intermediate during base-catalyzed tautomerization. This enolate is highly reactive and important in organic chemistry.
  • Why is the enolate ion considered important in organic chemistry?
    The enolate ion is important because it is a highly reactive intermediate that participates in many chemical reactions. It is a key focus in the study of carbonyl chemistry.
  • What type of environment is required for tautomerization to occur in ketones and aldehydes?
    Tautomerization occurs naturally in aqueous environments for ketones and aldehydes. Both acid and base catalysis can facilitate this process.
  • What structural feature characterizes the enol tautomer?
    The enol tautomer features an alcohol group directly attached to a double bond, forming a vinyl alcohol. This structure is distinct from the keto tautomer.