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Slides 2 through 8 introduce some aspects of ring strain.

Slides 2 through 8 introduce some aspects of ring strain. In alkanes, each methylene group contributes ~ -5 kcal/mole to heat of formation ( D H o f ). Based on the above observation, what would you predict the D H o f of cyclopropane to be?.

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Slides 2 through 8 introduce some aspects of ring strain.

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  1. Slides 2 through 8 introduce some aspects of ring strain.

  2. In alkanes, each methylene group contributes ~ -5 kcal/mole to heat of formation (DHof). Based on the above observation, what would you predict the DHof of cyclopropane to be?

  3. In science, if the data obtained doesn't fit the theory, what should be done? a. Ignore the data because it doesn’t fit my worldview. b. Give up. c. Determine whether the theory can be modified d. Discard the theory and start over. e. Either c. or d. depending on the circumstances. f. Change the data g. Cry

  4. Types of Strain 1. Angle Strain (Baeyer):  What is the nominal hybridrization in cyclopropane?  a. sp3 b. sp2 c. sp d. p sp3  What should the bond angles be? 109.5  What are the angles in an equilateral triangle? 60

  5. Types of Strain normal C-C bond internuclear axis  bent bond: less overlap Hybrid orbitals in bonds actually have more p character.

  6. Types of Strain • Which set of statements should be true if there is less orbital overlap in a bond? a. The bond will be weaker. The molecule will be less stable. Hf will be more negative. b. The bond will be stronger. The molecule will be more stable. Hf will be more negative. c. The bond will be weaker. The molecule will be more stable. Hf will be more negative. d. The bond will be weaker. The molecule will be less stable. Hf will be more positive. e. The bond will be stronger. The molecule will be more stable. Hf will be more positive.

  7. Types of Strain Torsional Strain What is it? a. Increase in PE due to poor overlap of p orbitals. b. Increase in PE due to orbitals having more p character. c. Increase in PE due to electron repulsion between electron clouds from eclipsing bonds. d. Decrease in PE due to better overlap of p orbitals.

  8. Types of Strain Are the C-H bonds in cyclopropane eclipsed? a. yes b. no c. no way to tell

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