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NEU Organic Chem 1 Warner Fall 2010 Exam 1
These flashcards comprise all of the questions and their answers from the Fall 2010 exam 1
Organic Chemistry
Undergraduate 1

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How many different diastereomers can there be from 1,2,4,5-tetramethylcyclohexane and how many of these diastereomers have 2 chair forms that have identical conformational energies?

  1. 4 diastereomers, 3 have equienergetic chair forms
  2. 5 diastereomers, 3 ""
  3. 4 ""                   2 ""
  4. 5 ""                   2 ""
  5. 6 ""                   3 ""

B, 5 diastereomers and 3 have equienergetic chair forms


Pick a pair for structures which represent diastereomers (one up-one down vs. both up or down) considering the following are found on cyclohexane:

  1. 1 axial chlorine, 4 equitorial bromine
  2. 1 axial chlorine, 4 equitorial bromine
  3. 1 axial chrloine, 4 equitorial bromine
  4. 1 axial bromine, 3 equitorial chlorine
  5. 1 axial chlorine, 3 equitorial bromine

A: 1 and 2 B: 1 and 4 C: 2 and 3 D: 4 and 5 E: none shown


There are no pairs of diastereomers since there is no single change that occurs as all changes presented occur together


Which of the following statements about heats of formation is correct?

  1. The heat of formatiosn is the entropy difference between a molecule and its constituent atoms in their elemental forms
  2. The heat of formation is the energy given off when a molecule is decomposed into its constituent atoms
  3. If 2 molecules have the same heat of formation, they must be identical
  4. If 2 isomers have the same heat of formation they must be identical
  5. The heat of formation of a particular compound may actually be negative as long as its atomization energy is positive

The following standard heats of formation (kcal/mol) have been measured: MeMe -20.1 MeCH2Me -25.0 Me3CH -32.1 Me4 -40.0 1,1-dimethylcyclohexane -43.2. Base on this information, what is the apparent strain energy of 1,1-dimethylcyclohexane?

  1. 1.2 kcal/mol
  2. 1.4 kcal/mol
  3. 1.6 kcal/mol
  4. 6.3 kcal/mol
  5. -1.6 kcal/mol

How many of the 35 constitutional isomers of the formula C9H20 have only secondary carbon atoms? 0, 1, 3, 4 or 5?


None do. It is impossible for a constitutional isomer of the C9H20 formula to be comprised of only secondary carbon atoms


Which statement about molecular orbitals (MO's) is incorrect?

  1. The sigma and pi electrons of ethene are completely separate but the same is not true for ethyne
  2. Sigma-pi e- interaction is called hyperconjugation
  3. Degenerate MO's are 2 or more MO's that have the same energy?
  4. The HOMOs of methane and ethane are delocalized over the entire molecule
  5. LUMO means the vacant MO with the lowest energy

Which of the following statements is incorrect about VB theory?

  1. Lines between 2 atoms represent 2 e-'s bonded
  2. A pair of dots next to an atom represents occupation of an antibonding orbital
  3. If you want several identical bonds to an atom the convention is to "rehybridize" certain atomic orbitals via a linear combination
  4. E- delocalization is accounted for by the addition of "resonance theory"
  5. The VB approach is particularly useful for representing structures on paper

Which of the following has the largest molecular dipole moment?

  1. (E)-1,2-dichloromethane
  2. Tetrachloromethane
  3. Bromomethane
  4. Difluoromethane
  5. Hexafluoroethane

Which of the following statements regarding nodes is correct?

  1. Nodes are almost always planar but occassionally the nodal plane is bent (like in a hybridized orbital)
  2. Nodes are places in space where the electronic wave function has a negative value
  3. The position of an atomic nucleus is always a node in any electronic wave function
  4. As you pass through a node the probability of finding an electron goes from positive to negative
  5. If a note exists in an atomic orbital it will always persist in any MO derived from that atomic orbital
An acid was 1% ionized at a pH of 4. What is its pKa? 2, 4, 5, 6 or 8?

Its pKa would be 6, D

The Ea's for the addition of HBr to ethene, but-2-ene and 2,3-dimethylbut-2-ene are 39, 29 and 24 respectively. Which of these would should the greatest rate increase upon raising the temperature or would they all show the same increase? Or is this impossible to determine?

Ethene, A, would show the largest increase


Which of the following contributes to make delta G (more free energy) for a reaction more positive?

  1. A more negative delta S
  2. A smaller Ea
  3. A larger rate constant
  4. A more negative delta H
  5. None of the above

A reaction of A+B gives C. 2 molecules of A slowly interact to form a reactive intermediate which rapidly reacts with B to give A and C. Which of the following observations would be uniquely consistent with the equation?

  1. The rate law was first order in [A] but was independent of [B]
  2. The reaction rate depended on both [A] and [B]
  3. The rate law was second order in [A] but was independent of [B]
  4. The half-life was independent of the concentration of any reactants
  5. The reaction rate increased as the temperature was increased

Pick the best answer with respect to the Arrhenius equation

  1. Transition state theory, which post-dates the derivation of the Arrhenius equation, demonstrates that the Arrhenius equation is invalid for most rxns
  2. When comparing rates at different temperatures, the Ea term cancels out
  3. The "A factor" is essentially the same as enthalpy of activation
  4. The basis for the Arrhenius equation is that the ratio of the forward rate to the reverse rate is the equilibrium constant for a system at equilibrium
  5. The energy of activation (Ea) is most similar to the entropy of activation term

Which of the following statements about 1,1,3,3-tetramethylcyclohexane is correct?

  1. It is destabilized by angle strain and torsional strain
  2. The H's are staggered but the C's are skew to each other
  3. It is destabilized by both steric and torsional strain
  4. Since it must contain a U-pentane interaction it is destabilized by torsional strain
  5. It is destabilized by steric strain only
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