Gibbs free energy differences between axial-substituted

Following are the structural formulas and names of four bicycloalkanes. Write the molecular formula of each compound. Which of these compounds are constitutional isomers?

For 1,2-dichloroethane: (a) Draw Newman projections for all eclipsed conformations formed by rotation from 0 to 360 about the carbon-carbon single bond. (b) Which eclipsed conformation(s) has (have) the lowest energy? Which has (have) the highest energy? (c) Which, if any, of these eclipsed conformations are related by refl ection?

Following is a chair conformation of cyclohexane with the carbon atoms numbered 1 through 6. 1 2 3 5 6 4 (a) Draw hydrogen atoms that are above the plane of the ring on carbons 1 and 2 and below the plane of the ring on carbon 4. (b) Which of these hydrogens are equatorial? Which are axial? (c) Draw the alternative chair conformation. Which hydrogens are equatorial? Which are axial? Which are above the plane of the ring? Which are below it?

Draw the alternative chair conformation for the trisubstituted cyclohexane given in Example 2.10. Label all CH3/H 1,3-diaxial interactions in this chair conformation.

Draw a chair conformation of 1,4-dimethylcyclohexane in which one methyl group is equatorial and the other is axial. Draw the alternative chair conformation, and calculate the ratio of the two conformations at 25C.

Which cycloalkanes show cis,trans isomerism? For each that does, draw the cis and trans isomers. (a) Methylcyclopentane (b) 1,1-Dimethylcyclopentane (c) 1,3-Dimethylcyclobutane

Following is a planar hexagon representation for one isomer of 1,2,4-trimethylcyclohexane. Draw the alternative chair conformations of this compound, and state which of the two is the more stable. H H H3C H CH3 CH3

Here is one cis,trans isomer of 3,5-dimethylcyclohexanol. Complete the alternative chair conformations. OH OH 1 3 3 5 5 1 CH3 H3C OH

Arrange the alkanes in each set in order of increasing boiling point. (a) 2-Methylbutane, 2,2- dimethylpropane, and pentane (b) 3,3-Dimethylheptane, 2,2,4-trimethylhexane, and nonane

Write a line-angle formula for each condensed structural formula. CH2CH3 CH3 CH3CH2CHCHCH2CHCH3 (a) CH2 CH3 (CH3)2 CH3 CH3CCH3 (b) (CH3)2CHCH(CH3)2 (c) CH2CH3 CH3CH2CCH2CH3 (d) (CH3) (e) 3CH CH3(CH2)3CH(CH3)2 (f) CH2CH3

Write the molecular formula of each alkane. (a) (b) (c)

Provide an even more abbreviated formula for each structural formula, using parentheses and subscripts. CH3 CH3CH2CH2CH2CH2CHCH3 (a) CH2CH2CH3 CH2CH2CH3 HCCH2CH2CH3 (b) CH2CH2CH3 CH2CH2CH3 CH3CCH2CH2CH2CH2CH3 (c

Which statements are true about constitutional isomers? (a) They have the same molecular formula. (b) They have the same molecular weight. (c) They have the same order of attachment of atoms. (d) They have the same physical properties.

Indicate whether the compounds in each set are constitutional isomers. O CH3CCH3 O (a) CH3CH2OH and CH3OCH3 (b) and CH3CH2CH O CH3COCH3 O and CH3CH2COH CH3CH2CH2CH2CH3 and OH CH3CHCH2CH3 O CH3CCH2CH3 (c) (d) and (e) CH2 CHCH2CH2CH3 (f) and

Each member of the following set of compounds is an alcohol; that is, each contains an !OH (hydroxyl group, Section 1.3A). Which structural formulas represent the same compound, and which represent constitutional isomers? OH (a) (b) OH (c) (d) OH OH OH OH HO (e) (f) OH (g) (h)

Each of the following compounds is an amine (Section 1.3B). Which structural formulas represent the same compound, and which represent constitutional isomers? NH2 NH2 NH2 H (b) NH (c) N N H (a) (d) H N (f) NH (g) 2 (e) (h)

Each of the following compounds is either an aldehyde or a ketone (Section 1.3C). Which structural formulas represent the same compound and which represent constitutional isomers? H H (b) (c) O O O O O O (a) O (d) (e) H (f) (g) (h) O

Draw structural formulas and write IUPAC names for the nine constitutional isomers with the molecular formula C7H16.

Draw structural formulas for all the following. (a) Alcohols with the molecular formula C4H10O (b) Aldehydes with the molecular formula C4H8O (c) Ketones with the molecular formula C5H10O (d) Carboxylic acids with the molecular formula C5H10O2

Write IUPAC names for these alkanes and cycloalkanes: (a) (b) (c) (d) (e)

Write structural formulas for the following alkanes and cycloalkanes. (a) 2,2,4-Trimethylhexane (b) 2,2-Dimethylpropane (c) 3-Ethyl-2,4,5-trimethyloctane (d) 5-Butyl-2,2-dimethylnonane (e) 4-(1- Methylethyl)octane (f) 3,3-Dimethylpentane (g) trans-1,3-Dimethylcyclopentane (h) cis-1,2- Diethylcyclobutane

Explain why each is an incorrect IUPAC name, and write the correct IUPAC name for the intended compound. (a) 1,3-Dimethylbutane (b) 4-Methylpentane (c) 2,2-Diethylbutane (d) 2-Ethyl-3- methylpentane (e) 2-Propylpentane (f) 2,2-Diethylheptane (g) 2,2-Dimethylcyclopropane (h) 1-Ethyl-5- methylcyclohexane

For each IUPAC name, draw the corresponding structural formula. (a) Ethanol (b) Butanal (c) Butanoic acid (d) Ethanoic acid (e) Heptanoic acid (f) Propanoic acid (g) Octanal (h) Cyclopentene (i) Cyclopentanol (j) Cyclopentanone (k) Cyclohexanol (l) Propanone

Write the IUPAC name for each compound. CH3CH2CCH3 O OH CH3CH2CH O O OH (a) (d) (e) (b) CH3CHCH3 (f) (c) CH3CH2CH2CH2CH2COH O (g) CH (h) 3CH CH2

Assume for the purposes of this problem that, to be an alcohol (-ol) or an amine (-amine), the hydroxyl or amino group must be bonded to a tetrahedral (sp3 hybridized) carbon atom. Write the structural formula of a compound with an unbranched chain of four carbon atoms that is an: (a) Alkane (b) Alkene (c) Alkyne (d) Alkanol (e) Alkenol (f) Alkynol (g) Alkanamine (h) Alkenamine (i) Alkynamine (j) Alkanal (k) Alkenal (l) Alkynal (m) Alkanone (n) Alkenone (o) Alkynone (p) Alkanoic acid (q) Alkenoic acid (r) Alkynoic acid

Torsional strain resulting from eclipsed C!H bonds is approximately 4.2 kJ (1.0 kcal)/ mol, and that for eclipsed C!H and C!CH3 bonds is approximately 6.3 kJ (1.5 kcal)/ mol. Given this information, sketch a graph of energy versus dihedral angle for propane.

How many different staggered conformations are there for 2-methylpropane? How many different eclipsed conformations are there?

Consider 1-bromopropane, CH3CH2CH2Br. (a) Draw a Newman projection for the conformation in which !CH3 and !Br are anti (dihedral angle 180). (b) Draw Newman projections for the conformations in which !CH3 and !Br are gauche (dihedral angles 60 and 300). (c) Which of these is the lowest energy conformation? (d) Which of these conformations, if any, are related by refl ection?

Consider 1-bromo-2-methylpropane, and draw the following. (a) The staggered conformation(s) of lowest energy (b) The staggered conformation(s) of highest energy

Trans-1,4-di-tert-butylcyclohexane exists in a normal chair conformation. Cis-1,4-di- tertbutylcyclohexane, however, adopts a twist-boat conformation. Draw both isomers, and explain why the cis isomer is more stable in a twist-boat conformation.

From studies of the dipole moment of 1,2-dichloroethane in the gas phase at room temperature (25C), it is estimated that the ratio of molecules in the anti conformation to gauche conformation is 7.6 to 1. Calculate the difference in Gibbs free energy between these two conformations.

Draw structural formulas for the cis and trans isomers of hydrindane. Show each ring in its most stable conformation. Which of these isomers is the more stable?

Following are the alternative chair conformations for trans-1,2-dimethylcyclohexane. (a) Estimate the difference in free energy between these two conformations. (b) Given your value in (a), calculate the percent of each chair present in an equilibrium mixture of the two at 25C. CH3 CH3 CH3 CH3

What structural feature of cycloalkanes makes cis,trans isomerism in them possible?

Is cis,trans isomerism possible in alkanes?

Draw structural formulas for the cis and trans isomers of 1,2-dimethylcyclopropane.

Name and draw structural formulas for all cycloalkanes with molecular formula C5H10. Be certain to include cis and trans isomers as well as constitutional isomers.

Using a planar pentagon representation for the cyclopentane ring, draw structural formulas for the cis and trans isomers of the following. (a) 1,2-Dimethylcyclopentane (b) 1,3-Dimethylcyclopentane

Gibbs free energy differences between axial-substituted and equatorial-substituted chair conformations of cyclohexane were given in Table 2.4. (a) Calculate the ratio of equatorial to axial tert-butylcyclohexane at 25C. (b) Explain why the conformational equilibria for methyl, ethyl, and isopropyl substituents are comparable but the conformational equilibrium for tert-butylcyclohexane lies considerably farther toward the equatorial conformation.

When cyclohexane is substituted by an ethynyl group, !C # CH, the energy difference between axial and equatorial conformations is only 1.7 kJ (0.41 kcal)/mol. Compare the conformational equilibrium for methylcyclohexane with that for ethynylcyclohexane, and account for the difference between the two.

Calculate the difference in Gibbs free energy in kilojoules per mole between the alternative chair conformations of: (a) trans-4-Methylcyclohexanol (b) cis-4-Methylcyclohexanol (c) trans-1,4- Dicyanocyclohexane

Draw the alternative chair conformations for the cis and trans isomers of 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, and 1,4-dimethylcyclohexane. (a) Indicate by a label whether each methyl group is axial or equatorial. (b) For which isomer(s) are the alternative chair conformations of equal stability? (c) For which isomer(s) is one chair conformation more stable than the other

Use your answers from Problem 2.48 to complete the table showing correlations between cis,trans and axial,equatorial for disubstituted derivatives of cyclohexane. Position of Substitution cis trans 1,4- a,e or e,a e,e or a,a 1,3- or or 1,2- or or

There are four cis,trans isomers of 2-isopropyl-5-methylcyclohexanol: OH 2-Isopropyl-5- methylcyclohexanol 5 2 1 (a) Using a planar hexagon representation for the cyclohexane ring, draw structural formulas for the four cis,trans isomers. (b) Draw the more stable chair conformation for each of your answers in part (a). (c) Of the four cis,trans isomers, which is the most stable? (Hint: If you answered this part correctly, you picked the isomer found in nature and given the name menthol.)

Draw alternative chair conformations for each substituted cyclohexane, and state which chair is more stable. (a) (b) H H HO OH HO H H H OH OH H H OH CH3 HO H H H CH2OH OH H OH (c) (d)

1,2,3,4,5,6-Hexachlorocyclohexane shows cis,trans isomerism. At one time a crude mixture of these isomers was sold as an insecticide. The insecticidal properties of the mixture arise from one isomer, known as lindane, which is cis-1,2,4,5-trans-3,6- hexachlorocyclohexane. (a) Draw a structural formula for 1,2,3,4,5,6-hexachlorocyclohexane disregarding, for the moment, the existence of cis,trans isomerism. What is the molecular formula of this compound? (b) Using a planar hexagon representation for the cyclohexane ring, draw a structural formula for lindane. (c) Draw a chair conformation for lindane, and label which chlorine atoms are axial and which are equatorial. (d) Draw the alternative chair conformation of lindane, and again label which chlorine atoms are axial and which are equatorial. (e) Which of the alternative chair conformations of lindane is more stable? Explain.

In Problem 2.24, you drew structural formulas for all isomeric alkanes with molecular formula C7H16. Predict which isomer has the lowest boiling point and which has the highest boiling point.

What generalization can you make about the densities of alkanes relative to the density of water?

What unbranched alkane has about the same boiling point as water? (Refer to Table 2.5 on the physical properties of alkanes.) Calculate the molecular weight of this alkane, and compare it with that of water.

Complete and balance the following combustion reactions. Assume that each hydrocarbon is converted completely to carbon dioxide and water. (a) Propane 1 O2 : (b) Octane 1 O2 : (c) Cyclohexane 1 O2 : (d) 2-Methylpentane 1 O2 :

Following are heats of combustion per mole for methane, propane, and 2,2,4-trimethylpentane. Each is a major source of energy. On a gram-for-gram basis, which of these hydrocarbons is the best source of heat energy? Hydrocarbon Component of DH0 [KJ (kcal)/mol] CH4 Natural gas 2891 (2213) CH3CH2CH3 LPG 22220 (2531) CH3CCH2CHCH3 CH3 CH3 CH3 Gasoline 25452 (21304)

Following are structural formulas and heats of combustion of acetaldehyde and ethylene oxide. Which of these compounds is the more stable? Explain. CH39CH Acetaldehyde ?1164 kJ (?278.8 kcal)/mol O H2C9CH2 Ethylene oxide ?1264 kJ (3 ? 02.1 kcal)/mol O

Without consulting tables, arrange these compounds in order of decreasing (less negative) heat of combustion: hexane, 2-methylpentane, and 2,2-dimethylbutane.

Which would you predict to have the larger (more negative) heat of combustion, cis-1,4- dimethylcyclohexane or trans-1,4-dimethylcyclohexane?

Following are structural formulas for 1,4-dioxane and piperidine. 1,4-Dioxane is a widely used solvent for organic compounds. Piperidine is found in small amounts in black pepper (Piper nigrum). O O 1,4- Dioxane Piperidine H N (a) Complete the Lewis structure of each compound by showing all unshared electron pairs. (b) Predict bond angles about each carbon, oxygen, and nitrogen atom. (c) Describe the most stable conformation of each ring, and compare these conformations with the chair conformation of cyclohexane

Following is a planar hexagon representation of l-fucose, a sugar component of the determinants of the A, B, O blood group typing. For more on this system of blood typing, see Connections to Biological Chemistry A, B, AB, and O Blood Types in Chapter 25. l-Fucose HO H HO H O OH CH3 OH H H H 1 3 2 4 5 (a) Draw the alternative chair conformations of l-fucose. (b) Which of them is the more stable? Explain

On the left is a stereorepresentation of glucose (we discuss the structure and chemistry of glucose in Chapter 25): (a) (b) O Glucose 1 1 2 2 3 3 5 5 4 4 OH CH2OH O HO OH HO 5 4 3 2 1 O (a) Convert the stereorepresentation on the left to a planar hexagon representation. (b) Convert the stereorepresentation on the left to a chair conformation. Which substituent groups in the chair conformation are equatorial? Which are axial?

Following is the structural formula and a ball-and-stick model of cholestanol. The only difference between this compound and cholesterol (Section 26.4) is that cholesterol has a carbon-carbon double bond in ring B. H HO A B C CH3 CH3 H D H H Cholestanol (a) Describe the conformation of rings A, B, C, and D in cholestanol. (b) Is the hydroxyl group on ring A axial or equatorial? (c) Consider the methyl group at the junction of rings A and B. Is it axial or equatorial to ring A? Is it axial or equatorial to ring B? (d) Is the methyl group at the junction of rings C and D axial or equatorial to ring C?

Following is the structural formula and a ball-and-stick model of cholic acid (Chapter 26), a component of human bile whose function is to aid in the absorption and digestion of dietary fats. H HO OH A B C CH3 CH3 H D OH H H COOH Cholic acid (a) What is the conformation of ring A? of ring B? of ring C? of ring D? (b) Are the hydroxyl groups on rings A, B, and C axial or equatorial to their respective rings? (c) Is the methyl group at the junction of rings A and B axial or equatorial to ring A? Is it axial or equatorial to ring B? (d) Is the hydrogen at the junction of rings A and B axial or equatorial to ring A? Is it axial or equatorial to ring B? (e) Is the methyl group at the junction of rings C and D axial or equatorial to ring C?