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3.12: Quiz 2B Key

  • Page ID
    19093
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    1. Clearly indicate true (T) or false (F) for the following statements (2 pts each):
    __T__ Cyclopropane has more ring strain than cyclohexane.
    __F__ A pi bond is stronger than a sigma bond.
    __T__ The staggered conformation of ethane is more stable than the eclipsed form of ethane because there is less strain and electron repulsion.
    __F__ Propyl ethyl ether is a molecule with 6 carbon atoms.
    1. Multiple Choice: (2 pts each)
      1. Which of the following statements about propene, CH3CH=CH2, is correct?
        1. B.pngAll nine atoms lie in the same plane
        2. All three carbon atoms lie in the same plane
        3. The compound has a cis and trans isomer
        4. All the carbon atoms are sp2 hybridized
      2. Which of the following is the strongest interaction?
        1. D.pnghydrogen bonding
        2. induced dipole-induced dipole interactions
        3. dipole-dipole interactions
        4. a covalent bond
        5. Van der Waals
      3. B.pngWhich of the following has the greatest van der Waal's interaction between molecules of the same kind?

    2iii.png

    1. C.pngWhich of the following has the greatest solubility in an organic solvent such as hexanes?


    1. D.pngWhich of the following has the greatest solublity in H2O?

    2v.png

      1. (5 pts) Example structures of the major components of gasoline, diesel and biodiesel are shown below. Indicate which will have the highest boiling point and briefly explain your answer.

    3a.png

    All three have van der Waal’s (induced dipole-induced dipole) interactions between molecules due to the hydrocarbon groups. But the biodiesel molecule also has the electronegative oxygen atoms that make the molecule polar so that there are also dipole-dipole interactions between the molecules (which are stronger than the van der Waal’s forces). Thus, the biodiesel will have a higher boiling point because more energy (temperature) is required to disrupt the stronger interactions. (see page 60-62, including problems and problem-solving strategy)

    (Note: biodiesel does NOT have hydrogen-bonding between its molecules because there is not an OH group. You have to have both the oxygen and the hydrogen in an alcohol group for hydrogen-bonding between its own molecules. For example an ether group has an oxygen, but it cannot have hydrogen-bonding between its molecules. However, an ether can still have hydrogen-bonding to water because there would be both the oxygen lone pair and also the O-H from water)

    1. (5 pts) Butanol is being favorably considered as an improved biofuel or fuel additive, while butylamine is not. The boiling point (and smell!) of the amine, might be part of this reason. Provide a brief explanation why butylamine has a lower boiling point than butanol.

    3b.png

    Both molecules have groups capable of hydrogenbonding, so you have to consider the strength of the hydrogen bonding between molecules. The oxygen is more electronegative so that the O-H bond has a stronger dipole. The stronger dipole means that the hydrogen bonding will be stronger between molecules with the OH group compared to the hydrogen-bonding between molecules with the NH group. (see page 60-62)

    1. (5 pts) Convert the flat bromo-cyclohexane structure shown below to a drawing of a chair conformation of cyclohexane with the Br group in an equatorial position. (You do not need to show hydrogens).

    4.png

    There are several different chair structures that are acceptable; here are some examples. Since there is only one Br group attached to the cyclohexane ring, the position of the Br does not matter.

    1. (6 pts) Provide a brief explanation why a C-C single bond can freely rotate but a C=C double bond cannot. Please include any relevant orbital drawing in your explanation.

      A C-C single bond can freely rotate because there is only a sigma bond with end-to-end overlap. A C=C double bond consists of a sigma bond and a pi bond. There are two p-orbitals that form the pi bond and these must have parallel overlap to form the pi bond. If you rotate a C=C double bond, the orbitals would not have parallel overlap and the pi bond would break. (see page 86)

    5.png

    1. (7 pts total) Each of the following compounds has important nutrition and health benefits. Resveratrol is an important antioxidant molecule found in the skin of grapes and a constituent of some wine. a-Linolenic acid (ALA) is an omega-3 fatty acid.
      1. Label whether each of the indicated alkenes in a-linolenic acid (ALA) is in the cis or trans form.

    6a.png

    1. Label whether the indicated alkene in resveratrol is the cis or trans form. Provide the name for the indicated functional group in resveratrol (in the answer box provided).

    6a.png

    1. Would you expect either of these molecules to have the same health effects if they were the opposite isomer? Briefly explain your answer.

      No, if either molecule was the opposite cis or trans isomer, then the molecule would be a different shape, and would be expected to have a different property.

      (Note: The cis isomer is not always healthier than trans isomer, or vice versa…it depends on the molecule. In the case of omega fatty acids and also lycopene, it turns out that cis has the desired health effects. But there are many cases, such as resveratrol, where the trans isomer has the desired biological effects.)

    1. Extra Practice:

    What intermolecular force do you think a gecko takes advantage of to stick to walls and windows?

    Van der Waal’s forces! Amazing! Apparently there is enough surface area for good amount of forces to build up to help the geck stick, and stronger forces like hydrogen-bonding and covalent bonds would mean that the gecko would stick too well and couldn’t move very quickly when it needed to.


    3.12: Quiz 2B Key is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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