Carbonyl Group and Reactions Quiz

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Questions and Answers

What characterizes an electrophile in a chemical reaction?

  • It readily accepts protons during a reaction.
  • It is a species that donates electrons.
  • It is rich in free electron pairs.
  • It contains an atom that is slightly positive. (correct)

What is the role of a nucleophile in reactions involving carbonyl compounds?

  • It donates an electron pair to form a bond. (correct)
  • It reacts with other nucleophiles.
  • It stabilizes the positive charge on the electrophile.
  • It acts as a leaving group.

How do thioesters behave in chemical reactions?

  • They can only react with alcohols.
  • They react with molecules that have available electron pairs. (correct)
  • They act as strong nucleophiles.
  • They are considered poor electrophiles.

Which of the following is true regarding leaving groups in chemical reactions?

<p>A good leaving group stabilizes a negative charge after departure. (B)</p> Signup and view all the answers

In the context of electrophilic reactions, what happens to the carbon atom in a carbonyl compound?

<p>It becomes slightly positive due to electronegative oxygen. (A)</p> Signup and view all the answers

Which groups can successfully act as leaving groups in carbonyl substitution reactions?

<p>Chlorine and sulfur groups (C)</p> Signup and view all the answers

Which of the following statements about nucleophiles is accurate?

<p>Neutral nucleophiles can lose a proton during reactions. (B)</p> Signup and view all the answers

In the context of substitution reactions, what role do electrophiles play?

<p>They react with nucleophiles by accepting electrons. (A)</p> Signup and view all the answers

Which of the following carbonyl compounds can undergo substitution reactions?

<p>Thioesters with good leaving groups (B)</p> Signup and view all the answers

What is necessary for a leaving group to effectively stabilize a negative charge in substitution reactions?

<p>It must contain heteroatoms that can stabilize it. (B)</p> Signup and view all the answers

Which is a correct representation of a substitution reaction at a carbonyl group?

<p>R-CO-X + :Nu -&gt; R-CO-Nu + X (C)</p> Signup and view all the answers

Which of the following best explains the behavior of thioesters in substitution reactions?

<p>They often result in the formation of more stable products. (A)</p> Signup and view all the answers

Which of these statements about carbonyl substitution reactions is incorrect?

<p>Methyl groups can act as leaving groups. (B)</p> Signup and view all the answers

What type of reaction occurs when aldehydes react with amines to form imines?

<p>Condensation (B)</p> Signup and view all the answers

What happens to imines when excess water is present?

<p>They hydrolyze to aldehydes or ketones (D)</p> Signup and view all the answers

Which statement accurately describes the role of NAD+ in alcohol oxidation?

<p>It acts as a hydride acceptor (B)</p> Signup and view all the answers

Which of the following is the product when ethanol is oxidized by Alcohol Dehydrogenase?

<p>Acetaldehyde (C)</p> Signup and view all the answers

How do secondary alcohol dehydrogenase enzymes function in bacteria?

<p>They reduce acetone to isopropanol (B)</p> Signup and view all the answers

Which term best describes the reaction where alcohol dehydrogenase enzymes convert alcohols to aldehydes?

<p>Oxidation (B)</p> Signup and view all the answers

What defines a condensation reaction involving the carbonyl group?

<p>It occurs with the loss of a water molecule (A)</p> Signup and view all the answers

In the context of carbonyl chemistry, what does the term 'reduction' refer to?

<p>Gaining electrons or hydrogens (B)</p> Signup and view all the answers

During the process of imine formation, what is the reason for the loss of water?

<p>It leads to the formation of a more stable compound (C)</p> Signup and view all the answers

What role do thioesters play in nucleophilic attack mechanisms?

<p>They serve as strong electrophiles (C)</p> Signup and view all the answers

Flashcards

Substitution Reaction (carbonyl)

A reaction where a group (X) on a carbonyl is replaced by a new group (Nu).

Leaving Group

A group (X) that departs from a molecule carrying a pair of electrons, stabilizing a negative charge.

Good Leaving Group

A leaving group that effectively stabilizes the negative charge, facilitating the reaction.

Nucleophile

An atom or molecule that donates a pair of electrons to form a new bond. (electron-loving).

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Electrophile

An atom or molecule that accepts a pair of electrons to form a new bond. (electron-seeking)

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Carbonyls that undergo substitution

The carbonyls with a suitable leaving group are substituted.

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Impossible Carbonyls for Substitution

Aldehydes and ketones with no substituent on the carbonyl cannot undergo substitution.

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Biological Substitution Reactions

Substitution reactions in living organisms happen with special leaving groups, like thioesters and acyl phosphates.

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Why is carbonyl an electrophile?

The carbon atom in a carbonyl group is slightly positive due to oxygen's higher electronegativity, making it an 'electron-lover' or electrophile.

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Thioester leaving group

A thioester group, which is a sulfur-containing ester, can act as a leaving group in carbonyl substitution reactions. It's often involved in biological reactions.

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Nucleophile in carbonyl substitution

The nucleophile is a molecule (like alcohol or amine) with electron-rich atoms that attack the electrophilic carbon in a carbonyl group, forming a new bond.

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What does 'good nucleophile' mean?

A good nucleophile readily donates its electron pair to form a new bond; it is strong and reactive. Amine nitrogen is, for example, a great nucleophile.

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Why does a carbonyl need a suitable leaving group?

A carbonyl can only undergo substitution if the group attached to the carbon is a good leaving group; it's capable of departing easily with the electron pair, making room for the nucleophile.

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Imine Formation

A reaction where an amine reacts with an aldehyde or ketone, forming an imine and releasing water.

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Imine Hydrolysis

The reverse of imine formation, where an imine reacts with water, breaking into an aldehyde or ketone and an amine.

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Condensation Reaction

A reaction where two molecules combine to form a larger molecule with the loss of a small molecule, often water.

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Vitamin B6 as a Cofactor

Vitamin B6 (pyridoxal) is an aldehyde that participates in imine formation with amino acids, facilitating their metabolism.

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Oxidation (Leo)

A chemical process where a molecule loses electrons or hydrogen atoms, gaining oxygen atoms.

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Reduction (RIG)

A chemical process where a molecule gains electrons or hydrogen atoms, losing oxygen atoms.

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Alcohol Dehydrogenase

An enzyme that catalyzes the oxidation of alcohols to aldehydes or ketones.

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NAD+ and NADPH

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme used in redox reactions as a hydride acceptor (oxidation). Its reduced form, NADPH, is a hydride donor (reduction).

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Secondary Alcohol Dehydrogenase

An enzyme that catalyzes the reduction of ketones to secondary alcohols.

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Substitution Reactions of Carbonyls

Reactions where a group attached to a carbonyl carbon is replaced by a new group.

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Study Notes

Carbonyl Group

  • The carbonyl group consists of a carbon atom double-bonded to an oxygen atom (C=O).
  • The general formula for a carbonyl group is R(C=O)R'.

Reactions of Aldehydes and Ketones

  • Imine formation from aldehydes and ketones: Aldehydes and ketones react with amines to form imines through a condensation reaction (water is lost).
  • Imine hydrolysis to aldehydes and ketones: Imines react with excess water to form their corresponding aldehydes or ketones and amines. Hydrolysis means splitting using water.
  • Alcohol oxidation to aldehydes and ketones: Alcohols can be oxidized to aldehydes or ketones using oxidizing agents. Loss of electrons/hydrogens (H).
  • Aldehyde or ketone reduction to alcohols: Aldehydes and ketones can be reduced to alcohols using reducing agents, gaining electrons/hydrogens (H).

Imine formation from aldehydes & amines

  • Amines react with aldehydes to form imines.
  • This reaction is a condensation reaction, hence water is lost.

Reverse reaction: Imine hydrolysis

  • Imines react with water to produce aldehydes/ketones and amines.

Imine formation from ketones & amines

  • Amines react with ketones to form imines.
  • This reaction is a condensation reaction, hence water is lost.

Reverse reaction: Imine hydrolysis

  • Imines react with water to give ketones/aldehydes and amines.

Imine formation is important in biology

  • A biological example is Vitamin B6 (pyridoxal)
  • Transaminase enzymes use pyridoxal (aldehyde) as a co-factor.

Redox reactions of Aldehydes & Ketones

  • Losing electrons (or H) is oxidation (LEO).
  • Gaining electrons is reduction (GER).

Ethanol is oxidised to acetaldehyde

  • This process occurs in the body through Alcohol Dehydrogenase (ADH).
  • NAD+ is used as an oxidizing agent, accepting hydrogens from ethanol and forming NADH.

Alcohol dehydrogenase enzymes

  • Alcohol dehydrogenase (ADH) enzymes catalyze the oxidation of alcohols using NAD+ as a coenzyme.
  • NAD+ accepts a hydrogen (H) and becomes NADH.

In bacteria, acetone is reduced to isopropanol.

  • This process occurs through Secondary Alcohol Dehydrogenase (SADH).

Substitution Reactions of Carbonyls

  • Substitution reactions occur when one of the two groups attached to the carbonyl is replaced by a new group.
  • Aldehydes and ketones do not undergo substitution at the carbonyl group.

Leaving Groups

  • Leaving groups are atoms or groups that can depart with a pair of electrons.
  • Good leaving groups stabilize their negative charge.
  • Examples include good leaving groups (SR, OPO3H2).

Neutral Nucleophiles

  • They lose a proton transferred to the leaving group in a reaction.

Electrophiles

  • Electrophiles are electron-loving species that can accept electrons.
  • Carbonyl groups are electrophiles.

Which of these contain good/poor/no leaving groups?

  • Carboxylic acid - poor
  • Ester - poor
  • Amide - poor
  • Acid anhydride - good
  • Acid chloride - good
  • Aldehyde - no
  • Ketone - no
  • Thioester - good
  • Mixed anhydride - good
  • Urea - poor

Summary/MCQ Test

  • Chemistry for the Biosciences (Crowe) material
  • Topics : nucleophiles, electrophiles, carbonyls, leaving groups, and redox reactions are included in the MCQ test.

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Lecture 10 - The Carbonyl Group - LS4002 - PDF

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