Q: Which of the following statements about the equilibrium between $$\text{N}_2\text{F}_4$$ and $$\text{NF}_2 is $$correct at room temperature?

$$\text{N}_2\text{F}_4 is $$favored, with only 0.7\% existing as $$\text{NF}_2.$$

Question 1

Given the experimental value for the chair-chair interconversion of trans-1,2-dimethylcyclohexane is $$\Delta G_{	ext{eq}} = -2.50$$ kcal/mol, and knowing that the gauche butane interaction is $$0.9$$ kcal/mol higher than the value calculated from the table, what is the best estimate for $$\Delta G_{	ext{eq}}$$ for 1,2-dimethylcyclohexane if both methyl groups are axial?

Accepted Answer

$$-3.05$$ kcal/mol

Question 2

Which of the following best explains why the axial methyl group in cyclohexane is less stable than the equatorial methyl group?

Accepted Answer

Axial methyl groups experience 1,3-diaxial interactions, increasing steric strain.

Question 3

If the free energy difference ($$\Delta G) $$for a conformational change is negative, what does this indicate about the relative stability of the two conformers?

Accepted Answer

The product conformer is more stable than the reactant conformer.

Question 4

Given the following substituent axial/equatorial free energy differences: $$	ext{CH}_3 = 1.74$$ kcal/mol, $$	ext{Br} = 0.55$$ kcal/mol, and $$	ext{Cl} = 0.40$$ kcal/mol, which substituent will most strongly prefer the equatorial position in cyclohexane?

Accepted Answer

$$	ext{CH}_3$$

Question 5

Which of the following is the correct Newman projection for the most stable conformation of 1,2-dimethylcyclohexane (trans isomer)?

Accepted Answer

Both methyl groups are equatorial and anti to each other.

Question 6

Which of the following best describes a 1,3-diaxial interaction in cyclohexane?

Accepted Answer

A steric interaction between an axial substituent and axial hydrogens on the same side of the ring.

Question 7

Which of the following is the correct IUPAC name for the compound with the structure shown as a bicyclic system with two bridges of length 1 and 2, and a total of 6 carbons?

Accepted Answer

bicyclo[2.2.1]hexane

Question 8

For the molecule (1R,2R,3R,5R)-1,2,3,5-tetramethylcyclohexane, which of the following best describes the correct way to draw its bond-line structure with correct wedge and dash notation?

Accepted Answer

Assign each chiral center with the correct stereochemistry, using wedges for bonds coming out of the plane and dashes for bonds going behind.

Question 9

Which of the following statements about the equilibrium between $$	ext{N}_2	ext{F}_4$$ and $$	ext{NF}_2 is $$correct at room temperature?

Accepted Answer

$$	ext{N}_2	ext{F}_4 is $$favored, with only 0.7\% existing as $$	ext{NF}_2.$$

Question 10

Which of the following best represents the arrow-pushing mechanism for the dissociation of $$	ext{N}_2	ext{F}_4 to $$two $$	ext{NF}_2$$ radicals?

Accepted Answer

A single-headed arrow from the N–N bond to each nitrogen atom, indicating homolytic cleavage.

Question 11

At 225°C, 97% of $$	ext{NF}_2 is $$found at equilibrium. What does this indicate about the sign of $$\Delta G$$ for the reaction $$	ext{N}_2	ext{F}_4 ightarrow 2\ 	ext{NF}_2 at $$this temperature?

Accepted Answer

$$\Delta G is $$negative, favoring product formation.

Question 12

Which of the following is true about the entropy change ($$\Delta S) $$for the reaction $$	ext{N}_2	ext{F}_4 ightarrow 2\ 	ext{NF}_2$$?

Accepted Answer

$$\Delta S is $$positive because two molecules are formed from one.

Question 13

Which of the following best describes a gauche interaction in butane?

Accepted Answer

A steric interaction between two methyl groups separated by three bonds in a staggered conformation.

Question 14

If the $$\Delta G$$ for a reaction is $$-3.05$$ kcal/mol, what is the equilibrium constant $$K at 298 K$$? (Use $$R = 1.987 	imes 10$$^{-3}$$ kcal/(mol·K))

Accepted Answer

$$K \approx 1.2 	imes 10^3$

Question 15

Which of the following is the correct Lewis structure for $$	ext{NF}_2$$ radical?

Accepted Answer

A nitrogen atom with two single bonds to fluorine atoms and one unpaired electron.

Thermodynamics and Conformational Analysis in Organic Chemistry

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