Compare the three staggered conformations of ethylene

The following substituent is called a phenyl group: Phenyl With this in mind, identify the systematic name for each substituent below

Draw all possible alkyl substituents that possess exactly five carbon atoms and no ring. Provide a systematic name for each of these substituents.

Provide a systematic name for each of the following compounds: (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m) (n) (o) (p) (q)

Draw a bond-line drawing for each of the following compounds: (a) 3-Isopropyl-2,4-dimethylpentane (b) 4-Ethyl-2-methylhexane (c) 1,1,2,2-Tetramethylcyclopropane

Name each of the following compounds: (a) (b) (c) (d) (e) (f) (g) (h) (i)

Draw a bond-line structure for each of the following compounds: (a) 2,2,3,3- Tetramethylbicyclo[2.2.1]heptane (b) 8,8-Diethylbicyclo[3.2.1]octane (c) 3- Isopropylbicyclo[3.2.0]heptane

4 For each pair of compounds, identify whether they are constitutional isomers or two representations of the same compound: (a) (b) (c) (d)

Table 4.4 indicates the number of constitutional isomers with molecular formula C7H16. Draw each of the isomers, making sure not to draw the same compound twice.

In each case below, draw a Newman projection as viewed from the angle indicated: (a) (c) (e) (b) (d) (f) Cl Cl Cl Cl Cl Cl Cl Br Observer Observer Observer Observer Observer

Draw a bond-line structure for each of the following compounds: (a) H CH2CH3 CH2CH3 CH3 CH3 CH3 (b) H H CH3 CH3 (c) H H H H H H H H

Determine whether the following compounds are constitutional isomers: H CH3 H H H H CH3 H H3C CH3 H

For each of the following compounds, predict the energy barrier to rotation (looking down any one of the C!C bonds). Draw a Newman projection and then compare the staggered and eclipsed conformations. Remember that we assigned 4 kJ/mol to each pair of eclipsing Hs and 6 kJ/mol to an H eclipsing a methyl group: (a) 2,2-Dimethylpropane (b) 2-Methylpropane

In each case below, identify the highest and lowest energy conformations. In cases where two or three conformations are degenerate, draw only one as your answer. (a) (b) (c) (d)

Compare the three staggered conformations of ethylene glycol. The anti conformation of ethylene glycol is not the lowest energy conformation. The other two staggered conformations are actually lower in energy than the anti conformation. Suggest an explanation.

Practice drawing a chair several times using a blank piece of paper. Repeat the procedure until you can do it without looking at the instructions above. For each of your chairs, make sure that it contains three sets of parallel lines.

Draw a chair conformation for each of the following compounds: (a) N H (b) O O

Practice drawing a chair conformation with all six axial positions. Repeat until you can draw all six positions without looking at the instructions above.

Practice drawing a chair conformation with all six equatorial positions. Repeat until you can draw all six positions without looking at the instructions above.

Practice drawing a chair conformation with all 12 positions (6 axial and 6 equatorial). Practice several times on a blank piece of paper. Repeat until you can draw all 12 positions without looking at the instructions above.

In the following compound, identify the number of hydrogen atoms that occupy axial positions as well as the number of hydrogen atoms that occupy equatorial positions:

Draw both chair conformations for each of the following compounds: (a) OH (b) NH2 (c) Cl (d) (e)

Consider the following chair conformation of bromocyclohexane: H H H H H Br H H (a) Identify whether the bromine atom occupies an axial position or an equatorial position in the conformation above. (b) Draw a bond-line drawing of this chair conformation (without Newman projections). (c) Draw a bond-line drawing of the other chair conformation (after a ring flip)

The most stable conformation of 5-hydroxy-1,3-dioxane has the OH group in an axial position, rather than an equatorial position. Provide an explanation for this observation.

Draw both conformations for each of the following compounds: (a) (b) (c) Br (d) Br (e) (f) (g) (h)

Lindane (hexachlorocyclohexane) is an agricultural insecticide that can also be used in the treatment of head lice. Draw both chair conformations of lindane. Cl Cl Cl Cl Cl Cl Lindane

Draw the lowest energy conformation for each of the following compounds: (a) (b) (c) Cl Cl (d) (e

In Problem 4.32, you drew the two chair conformations of lindane. Carefully inspect them and predict the difference in energy between them, if any. 4.35 Compound A exists predominantly in a chair conformation, while compound B exists predominantly in a twist boat conformation. Explain. Compound A Compound B

Compound A exists predominantly in a chair conformation, while compound B exists predominantly in a twist boat conformation. Explain. Compound A Compound B

6 Draw Haworth projections for cis-1,3-dimethylcyclohexane and trans-1,3-dimethylcyclohexane. Then, for each compound, draw the two chair conformations. Use these conformations to determine whether the cis isomer or the trans isomer is more stable

Draw Haworth projections for cis-1,4-dimethylcyclohexane and trans-1,4-dimethylcyclohexane. Then for each compound, draw the two chair conformations. Use these conformations to determine whether the cis isomer or the trans isomer is more stable.

Draw Haworth projections for cis-1,3-di-tert-butylcyclohexane and trans-1,3-di-tert-butylcyclohexane. One of these compounds exists in a chair conformation, while the other exists primarily in a twist boat conformation. Offer an explanation.

Identify the name of the parent for each of the following compounds: (a) (b) (c) (d)

Each of the structures in the previous problem has one or more substituents connected to the parent. (a) Identify the name of each substituent in 4.39a. (b) Identify the common name and the IUPAC name of the complex substituent in 4.39b. (c) Identify the name of each substituent in 4.39c. (d) Identify the common name and the IUPAC name of the complex substituent in 4.39d.

What is the systematic name for each of the following compounds: (a) (b) (c) (d)

For each of the following pairs of compounds, identify whether the compounds are constitutional isomers or different representations of the same compound: (a) (b) (c)

Use a Newman projection to draw the most stable conformation of 3-methylpentane, looking down the C2!C3 bond.

Identify which of the following compounds is expected to have the larger heat of combustion:

Draw each of the following compounds: (a) 2,2,4-Trimethylpentane (b) 1,2,3,4- Tetramethylcycloheptane (c) 2,2,4,4-Tetraethylbicyclo[1.1.0]butane

Sketch an energy diagram that shows a conformational analysis of 2,2-dimethylpropane. Does the shape of this energy diagram more closely resemble the shape of the energy diagram for ethane or for butane?

What are the relative energy levels of the three staggered conformations of 2,3-dimethylbutane when looking down the C2!C3 bond?

Draw the ring flip for each of the following compounds: (a) OH Cl (b) Cl OH (c) OH

For each of the following pairs of compounds, identify the compound that would have the higher heat of combustion: (a) (b) (c) (d)

Draw a relative energy diagram showing a conformational analysis of 1,2-dichloroethane. Clearly label all staggered conformations and all eclipsed conformations with the corresponding Newman projections.

Assign IUPAC names for each of the following compounds: (a) H H H CH3 H (b) H H H H CH3 H H H (c) H H CH3 H (d) H H CH3 CH3

The barrier to rotation of bromoethane is 15 kJ/mol. Based on this information, determine the energy cost associated with the eclipsing interaction between a bromine atom and a hydrogen atom.

Menthol, isolated from various mint oils, is used in the treatment of minor throat irritation. Draw both chair conformations of menthol and indicate which conformation is lower in energy. OHMenthol

Draw both chair conformations for each of the following compounds. In each case, identify the more stable chair conformation: (a) Methylcyclohexane (b) trans-1,2-Diisopropylcyclohexane (c) cis-1,3- Diisopropylcyclohexane (d) trans-1,4-Diisopropylcyclohexane

For each of the following pairs of compounds, determine which compound is more stable (you may find it helpful to draw out the chair conformations): (a) (b) (c) (d)

Draw a Newman projection of the following compound as viewed from the angle indicated: Cl Br Cl B

Glucose (a sugar) is produced by photosynthesis and is used by cells to store energy. Draw the most stable conformation of glucose:OHO OHHOOHOHGlucose

Sketch an energy diagram showing a conformational analysis of 2,2,3,3-tetramethylbutane. Use Table 4.6 to determine the energy difference between staggered and eclipsed conformations of this compound.

Rank the following conformations in order of increasing energy: H H Br H H Br Br H H Br H H Br Br H H H H Br H H H H B

Consider the following two conformations of 2,3-dimethylbutane. For each of these conformations, use Table 4.6 to determine the total energy cost associated with all torsional strain and steric strain. (a) CH3 CH3 CH3 H CH3 H (b) CH3 CH3 HCH3 H3C H

myo-Inositol is a polyol (a compound containing many OH groups) that serves as the structural basis for a number of secondary messengers in eukaryotic cells. Draw the more stable chair conformation of myo-inositol. OH HO OH HO OH OH

Below is the numbered skeleton of trans-decalin: 1 2 3 4 5 6 7 8 9 10 Identify whether each of the following substituents would be in an equatorial position or an axial position: (a) A group at the C-2 position, pointing UP (b) A group at the C-3 position, pointing DOWN (c) A group at the C-4 position, pointing DOWN (d) A group at the C-7 position, pointing DOWN (e) A group at the C-8 position, pointing UP (f) A group at the C-9 position, pointing UP

Propylene is produced by cracking petroleum and is a very useful precursor in the production of many useful polymers. Propylene has one constitutional isomer. Draw that isomer and identify its systematic name. Propylene

trans-1,3-Dichlorocyclobutane has a measurable dipole moment. Explain why the individual dipole moments of the C!Cl bonds do not cancel each other to produce a zero net dipole moment. trans-1,3- Dichlorocyclobutane Cl Cl

Do you expect cyclohexene to adopt a chair conformation? Why or why not? Explain. Cyclohexene

For each pair of compounds below, determine whether they are identical compounds, constitutional isomers, stereoisomers, or different conformations of the same compound: (a) H H CH3 CH3 H3C CH2CH3 CH2CH3 CH2CH3 H H H (b) (c) (d) (e) CH3 CH3 H H H H CH3 CH3 (f) CH3 CH3 H H H CH3 H CH3 (g) (h) H H H H H H CH3 CH3 (i) H H CH3 CH3 CH3 CH3 H H CH3 CH3 H3C CH3 (j) H H CH3 CH3 CH3 CH3 H H CH3 CH3 H3C CH3 (k) (l

Consider the structures of cis-1,2-dimethylcyclopropane and trans-1,2-dimethylcyclopropane: (a) Which compound would you expect to be more stable? Explain your choice. (b) Predict the difference in energy between these two compounds.

Consider the following tetra-substituted cyclohexane: OH Cl (a) Draw both chair conformations of this compound. (b) Determine which conformation is more stable. (c) At equilibrium, would you expect the compound to spend more than 95% of its time in the more stable chair conformation?

Consider the structures of cis-decalin and trans-decalin: cis-Decalin H trans-Decalin H H H (a) Which of these compounds would you expect to be more stable? (b) One of these two compounds is incapable of ring flipping. Identify it and explain your choice.

A biosynthetic pathway was recently proposed for the polycyclic, cytotoxic compound aspernomine, isolated from the fungus Aspergillus nomius (J. Am. Chem. Soc. 2012, 134, 80788081): Me Me OH HN O H Aspernomine (a) Two of the six-membered rings are represented in chair conformations. Is the connection between these two rings analogous to that in cis- or trans-decalin? (b) What is the approximate dihedral angle between the two methyl groups directly bound to the chairs? (c) Is the aromatic ring in an axial or equatorial position? (d) Consider the six-carbon acyclic substituent bound to one of the bridgehead carbons. What is its relationship (axial or equatorial) to each of the chairs?

Draw all three staggered conformations for the following compound, viewed along the C2!C3 bond. Determine which conformation is the most stable, taking into account gauche interactions and hydrogen-bonding interactions (J. Phys. Chem. A 2001, 105, 6991 6997). Provide a reason for your choice by identifying all of the interactions that led to your decision. H3C HO H OH H CH3 C2 C3

The conformations of methanol, viewed along the C!O bond, include both the staggered and the eclipsed forms, just as discussed in the case for ethane. The barrier for interconversion between these two conformations has been determined to be approximately 4.2 kJ/mol (or 1 kcal/mol) (J. Phys. Chem. A 2002, 106, 16421646). (a) Draw a Newman projection for each conformation. (b) Determine the energy cost (amount of torsional strain) associated with the eclipsing interaction between a lone pair and a C!H bond.

The following compound was designed as a molecular switch, in that it can be induced to access any of the four orientations shown (14) using pH as a switch (Org. Lett. 2011, 13, 3033). Describe the changes in (i) bonding and (ii) conformation and (iii) intramolecular hydrogen bonding shown as this compound is converted from 1 S 2 S 3 S 4: N N N N O O Acid N N N Acid Base O O N H N N O O N N H H H 1 2 3 4 N N N O O N H H H ! ! !

Organic compounds with extended regions of consecutive sp2 - hybridized atoms will sometimes exhibit an ability to absorb UV light and subsequently emit visible light, a property called fluorescence. We will explore a related phenomenon (absorbance in UV/visible wavelengths) in Chapter 17. The compound below (R = polyether group) is known to be fluorescent (J. Org. Chem. 2012, 77, 74797486): NN N N N N N N R R NN N N N N N N R R Planar conformation A Planar conformation B (a) Identify the s bonds that must undergo free rotation in order for conformation A to be converted into conformation B and describe what happens to the geometry of the molecule during this conformational change. (b) Conformation A is more stable than conformation B by 8.96 kcal/ mol. Propose an explanation for this observation.

The conformations of (+)-epichlorohydrin (1), viewed along the Ca!Cb bond, can be analyzed in exactly the same manner as the acyclic alkanes discussed in Chapter 4 (J. Phys. Chem. A 2000, 104, 61896196). (a) Draw all staggered conformations for 1 viewed along this bond. (b) Identify the least stable staggered conformation for 1. Challenge Problems 191 (c) The most stable conformation of 1,2-dichloropropane exhibits a methyl group that is anti to a chlorine atom. Using this information, identify the most stable conformation of 1 and justify your choice. Cb Ca O CH2 H Cl H H 1

The all-trans-1,2,3,4,5,6-hexaethylcyclohexane (1) prefers the all-equatorial conformation while the all-trans-1,2,3,4,5,6-hexaisopropylcyclohexane (2) possesses a severely destabilized all-equatorial conformation (J. Am. Chem. Soc. 1990, 112, 893894): Et Et Et Et Et Et i-Pr i-Pr i-Pr i-Pr i-Pr i-Pr 1 2 (a) By examining a molecular model of cyclohexane with several alltrans-equatorial isopropyl groups and another model with several all-trans-equatorial ethyl groups, determine why adjacent equatorially oriented isopropyl groups experience severe steric interactions which are lacking in the ethyl case. Draw a chair conformation of the former case which illustrates these severe steric interactions. Also draw a Newman projection looking down one of the C!C bonds connecting the cyclohexyl ring to an equatorial isopropyl group and illustrate a conformation with severe steric strain. (b) The all-axial conformation of 2 possesses a fairly stable conformation where the steric repulsion among the axial isopropyl groups can be minimized. Again, use models to examine this chair conformation and draw it. Also, draw a Newman projection looking down one of the C!C bonds connecting the cyclohexyl ring to an axial isopropyl group and illustrate why this conformation is lower than the all-equatorial chair conformation in steric destabilization.

Alkyne 1 can adopt the coplanar conformation 1a or the perpendicular conformation 1b (Chem. Rev. 2010, 110, 53985424). Predict which form is more favorable for 1 and provide a complete explanation for your choice. N C C B H H H H N C C B H H H H 1a 1b

The structural unit below has been incorporated into a synthetic polymer designed to mimic the skeletal muscle protein titin (J. Am. Chem. Soc. 2009, 131, 87668768). In its most stable conformation (not the one shown), it forms one intramolecular hydrogen bond and four intermolecular hydrogen bonds to an identical unit in the same conformation. Draw two equivalents of this molecule and clearly show all of the interactions described above. N N O H N H N O R R H R

Compounds 1 and 2 were prepared, and the difference in their respective heats of combustion was found to be 17.2 kJ/mol (J. Am. Chem. Soc. 1961, 83, 606614): O H H O 1 O H H O 2 (a) Redraw compounds 1 and 2 showing chair conformations for the six-membered rings. In each case, draw the lowest energy conformation for the compound. (b) Identify which compound has the larger heat of combustion. Explain your reasoning.