ACS CP Organic, Inorganic & Physical Chemistry 3

Question 1

What is the hybridization of the central boron atom in BF₃?

Accepted Answer

sp²

Answer

Boron in BF₃ has three bonding pairs and no lone pairs, resulting in trigonal planar geometry and sp² hybridization.

Question 2

Which of the following correctly describes the rate law for an SN2 reaction?

Accepted Answer

Rate = k[substrate][nucleophile]

Answer

SN2 reactions are second-order overall, with the rate depending on both the substrate and the nucleophile concentrations.

Question 3

In the Born-Haber cycle for NaCl, which step involves the largest energy release?

Accepted Answer

Lattice energy formation

Answer

Lattice energy formation releases the most energy in the Born-Haber cycle because of strong electrostatic interactions in the ionic crystal.

Question 4

According to the Arrhenius equation, a plot of ln(k) vs 1/T gives a straight line. What does the y-intercept represent?

Accepted Answer

ln(A)

Answer

The Arrhenius equation ln(k) = ln(A) - Ea/R × (1/T) shows the y-intercept equals ln(A), where A is the pre-exponential factor.

Question 5

Which spectroscopic technique is most useful for determining the carbon skeleton connectivity in an unknown organic molecule?

Accepted Answer

¹³C NMR spectroscopy

Answer

¹³C NMR, especially DEPT and 2D techniques like HMBC, directly reveals carbon environments and connectivity in organic molecules.

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