Question 1

Which of the following statements best describes a homolytic bond cleavage in an organic reaction?

Accepted Answer

Both atoms involved in the bond each take one electron from the bond, forming two radicals. $$A:B \rightarrow A$$^{\cdot}$$ + B$$^{\cdot}$$

Question 2

In the mechanism of the addition of HBr to ethene, which intermediate is formed after the first step?

Accepted Answer

A carbocation intermediate with 6 valence electrons on the central carbon. $$\ce{CH2=CH2 + HBr \rightarrow [CH3-CH2]^+ + Br^-}$$

Question 3

Which of the following best describes a nucleophile in organic chemistry?

Accepted Answer

A species rich in electrons, often with a negative charge or lone pairs, that donates an electron pair to form a new bond.

Question 4

Which of the following energy diagrams represents an exergonic reaction?

Accepted Answer

A diagram where the products are at a lower energy level than the reactants, with $$\Delta G \u003c 0.$$

Question 5

During a heterolytic bond cleavage, what type of intermediates can be formed?

Accepted Answer

Carbocations and carbanions, depending on which atom retains the electron pair.

Question 6

Which of the following is a correct representation of the movement of electrons in a polar reaction mechanism using curved arrows?

Accepted Answer

A curved arrow starts at a lone pair or a bond and points to the atom that will accept the electrons.

Question 7

Which of the following best describes the rate-determining step in a multi-step reaction mechanism?

Accepted Answer

The step with the highest activation energy ($$E_a) in $$the reaction pathway.

Question 8

Which of the following is an example of a condensation reaction in organic chemistry?

Accepted Answer

Two molecules combine to form a larger molecule with the elimination of a small molecule such as water. $$A-H + B-OH \rightarrow A-B + H_2O$$

Question 9

Which of the following statements about reaction intermediates is correct?

Accepted Answer

Carbocations have 6 electrons in their valence shell and are positively charged.

Question 10

Which of the following best describes an elimination reaction?

Accepted Answer

A reaction in which two atoms or groups are removed from a molecule, resulting in the formation of a double or triple bond.

Question 11

In a reaction energy diagram, what does the highest point along the reaction coordinate represent?

Accepted Answer

The transition state, which is the point of highest energy between reactants and products.

Question 12

Which of the following is a correct statement about exergonic and endergonic reactions?

Accepted Answer

Exergonic reactions have $$\Delta G  0$$ and are non-spontaneous.

Question 13

Which of the following is a characteristic of a nucleophilic substitution reaction (S$$_N$$)?

Accepted Answer

An atom or group in a molecule is replaced by a nucleophile.

Question 14

Which of the following best describes the role of a catalyst in an organic reaction?

Accepted Answer

It lowers the activation energy ($$E_a) of $$the reaction, increasing the reaction rate without being consumed.

Question 15

Which of the following is a correct example of a redox reaction in organic chemistry?

Accepted Answer

The oxidation of a primary alcohol to an aldehyde: $$\ce{R-CH2OH + [O] \rightarrow R-CHO + H2O}$$

Question 16

Which of the following is true about the use of curved arrows in reaction mechanisms?

Accepted Answer

Curved arrows show the movement of electron pairs from nucleophiles to electrophiles.

Question 17

Which of the following is a correct statement about the stability of reaction intermediates?

Accepted Answer

Carbocations are stabilized by alkyl groups through hyperconjugation and inductive effects.

Question 18

Which of the following best describes a rearrangement (transposition) reaction?

Accepted Answer

A reaction in which a molecule undergoes a reorganization of bonds and atoms to form an isomer.

Question 19

Which of the following is a correct example of a Lewis acid-base reaction?

Accepted Answer

A Lewis base donates an electron pair to a Lewis acid to form a coordinate covalent bond. $$\ce{NH3 + BF3 \rightarrow NH3BF3}$$

Question 20

Which of the following factors does NOT directly affect the rate of an organic reaction?

Accepted Answer

The color of the reactants.

Introducción y Mecanismos de las Reacciones Orgánicas

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