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Exam 2: Alkanes

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Question 21

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Which of the following statements about ethane is false?

A) Staggered ethane is destabilized by interactions between filled C-H σ and empty C-H σ* orbitals.
B) Staggered ethane is stabilized by interactions between filled C-H σ and empty C-H σ* orbitals.
C) All staggered conformations are identical in energy, and all eclipsed conformations are identical in energy.
D) The eclipsed conformation of ethane is an energy maximum between staggered conformations.
E) The eclipsed conformation is stabilized by interactions between filled C-H σ bonds.

F) None of the above
G) A) and E)

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Question 22

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Which of the following statements about methane, CH₄ , is false?

A) The carbon-hydrogen bonds in methane are formed by the combination of an sp³ orbital on carbon and a 1s orbital on hydrogen.
B) The CH bonding molecular orbital has cylindrical symmetry.
C) The CH antibonding molecular orbital does not have cylindrical symmetry.
D) The hybrid orbitals on carbon are 25% s character and 75 % p character.
E) All bond angles are 109.5°.

F) A) and B)
G) A) and C)

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Question 23

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How many ¹³C NMR signals would be observed for 3 -ethyl-4-methyloctane?

The quatenary carbon atom in the structure below is atom:

Draw a molecule with the molecular formula C₅H₁₀ that will show four signals in a ¹³C spectrum. A) B) C) D) E)

Which of the following line structures corresponds to the Lewis structure shown here?

Draw Newman projections of all the staggered conformations of butane looking down the C2-C3 bond, and state which of them is the lowest in energy.

Pure water at 25°C undergoes autoionization: Using curved arrow formalism, draw a mechanism for the transfer of a proton from one water molecule to another to form a hydroxide ion and a hydronium ion. Show all lone pairs of electrons and nonzero formal charges.

Which of these structures represent the same compound?

Draw and provide systematic names for all the constitutional isomers of C₄H₉Cl where the chlorine atom is attached to a primary carbon.

Which of the following structures would show more than two signals on a ¹H NMR spectrum?

How many signals will be seen in the 1H NMR spectrum for the following molecule? What will be the relative sizes of these signals?

What orbitals are involved from carbon and hydrogen to form each of the C-H bonds in acetylene?

Dibromocarbene is an example of a chemical species called a carbene Carbenes exist in one of two forms. In one of these forms, called a singlet, both of the nonbonding electrons on carbon occupy the same orbital. Approximately what type of orbital does the lone pair occupy?

In which of the following molecules can a methyl group be eclipsed either by a chlorine atom or by a bromine atom?

Which compounds would exhibit three peaks in a ¹³C NMR spectrum?

Using curved arrow formalism, draw a mechanism for the transfer of a proton from acetic acid, CH₃COOH, to methylamine, CH₃NH₂. Draw the products of the reaction and show all lone pairs of electrons and nonzero formal charges.

What is the approximate hybridization of each of the indicated carbon atoms in the structures shown here?

Which of the following statements is (are) true concerning the three molecules shown? I. The three molecules are constitutional isomers. II. Structure C is properly named as a hexane. III. Structure B has the highest boiling point of the three molecules. IV. Structure A has the highest boiling point of the three molecules.

Which molecule contains a ketone?