Solutions Manual For

Solutions Manual For Chemistry 11 th Edition By Steven Zumdahl, Susan Zumdahl, Donald DeCoste

(All Chapters 1-22, 100% Original Verified, A+ Grade)

All Chapters Arranged Reverse:

22-1 This is The Original Solutions Manual For 11 th Edition, All other Files in The Market are Fake/Old/Wrong Edition. 1 / 4

1048

CHAPTER 22

ORGANIC AND BIOLOGICAL MOLECULES

Review Questions

• A hydrocarbon is a compound composed of only carbon and hydrogen. A saturated hydro-

carbon has only carbon-carbon single bonds in the molecule. An unsaturated hydrocarbon has one or more carbon-carbon multiple bonds but may also contain carbon-carbon single bonds.A normal hydrocarbon has one chain of consecutively bonded carbon atoms, with each carbon atom in the chain bonded to one or two other carbon atoms. A branched hydrocarbon has at least one carbon atom in the structure that forms bonds to three or four other carbon atoms; the structure is not one continuous chain of carbon atoms.

An alkane is a saturated hydrocarbon composed of only C−C and C−H single bonds. Each carbon in an alkane is bonded to four other atoms (either C or H atoms). If the compound contains a ring in the structure and is composed of only C−C and C−H single bonds, then it is called a cyclic alkane.

Alkanes: general formula = CnH2n + 2; all carbons are sp

3 hybridized; bond angles = 109.5˚

Cyclic alkanes: general formula CnH2n (if only one ring is present in the compound); all carbons are sp 3 hybridized; prefers 109.5˚ bond angles, but rings with three carbons or four carbons or five carbons are forced into bond angles less than 109.5˚.

In cyclopropane, a ring compound made up of three carbon atoms, the bond angles are forced into 60˚ in order to form the three-carbon ring. With four bonds to each carbon, the carbons prefer 109.5˚ bond angles. This just can’t happen for cyclopropane. Because cyclopropane is forced to form bond angles smaller than it prefers, it is very reactive.

The same is true for cyclobutane. Cyclobutane is composed of a four-carbon ring. To form a ring compound with four carbons, the carbons in the ring are forced to form 90˚ bond angles; this is much smaller than the preferred 109.5˚ bond angles.

Cyclopentane (five-carbon rings) also has bond angles slightly smaller than 109.5˚, but they are very close (108˚), so cyclopentane is much more stable than cyclopropane or cyclobutane.For rings having six or more carbons, the observed bonds are all 109.5˚.

Straight chain hydrocarbons just indicates that there is one chain of consecutively bonded C- atoms in the molecule. They are not in a straight line which infers 180˚ bond angles. The bond angles are the predicted 109.5˚.

To determine the number of hydrogens bonded to the carbons in cyclic alkanes (or any alkane where they may have been omitted), just remember that each carbon has four bonds. In cycloalkanes, only the C−C bonds are shown. It is assumed you know that the remaining bonds on each carbon are C−H bonds. The number of C−H bonds is that number required to give the carbon four total bonds. 2 / 4

CHAPTER 22 ORGANIC AND BIOLOGICAL MOLECULES 1049

• Alkenes are unsaturated hydrocarbons that contain a carbon-carbon double bond. Carbon-

carbon single bonds may also be present. Alkynes are unsaturated hydrocarbons that contain a carbon-carbon triple bond.

Alkenes: CnH2n is the general formula. The carbon atoms in the C=C bond exhibit 120˚ bond angles. The double-bonded carbon atoms are sp 2 hybridized. The three sp 2 hybrid orbitals form three sigma bonds to the attached atoms. The unhybridized p atomic orbital on each sp 2

hybridized carbon overlap side to side to form the  bond in the double bond. Because the p orbitals must overlap parallel to each other, there is no rotation in the double bond (this is true whenever  bonds are present). See Figure 22.7 for the bonding in the simplest alkene, C2H4.

Alkynes: CnH2n – 2 is the general formula. The carbon atoms in the C−C bond exhibit 180˚ bond angles. The triple bonded carbons are sp hybridized. The two sp hybrid orbitals form two sigma bonds to the bonded atoms. The two unhybridized p atomic orbitals overlap with two unhybridized p atomic orbitals on the other carbon in the triple bond, forming two  bonds. If the z-axis is the internuclear axis, then one  bond would form by parallel overlap of py orbitals on each carbon and the other  bond would form by parallel overlap of px orbitals. As is the case with alkenes, alkynes have restricted rotation due to the  bonds. See Figure 22.10 for the bonding in the simplest alkyne, C2H2.

Any time a multiple bond or a ring structure is added to a hydrocarbon, two hydrogens are lost from the general formula. The general formula for a hydrocarbon having one double bond and one ring structure would lose four hydrogens from the alkane general formula. The general formula would be CnH2n – 2.

• Aromatic hydrocarbons are a special class of unsaturated hydrocarbons based on the benzene

ring. Benzene has the formula C6H6. It is a planar molecule (all atoms are in the same plane).The bonding in benzene is discussed in detail in Section 9.5 of the text. Figures 9.46, 9.47, and 9.48 detail the bonding in benzene.

C6H6, has 6(4) + 6(1) = 30 valence electrons. The two resonance Lewis structures for benzene

are:

These are abbreviated as:

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1050 CHAPTER 22 ORGANIC AND BIOLOGICAL MOLECULES

Each carbon in benzene is attached to three other atoms; it exhibits trigonal planar geometry with 120° bond angles. Each carbon is sp 2 hybridized. The sp 2 hybrid orbitals form three sigma bonds to each carbon. The unhybridized p atomic orbital on each carbon overlap side to side with unhybridized p orbitals on adjacent carbons to form the  bonds. All six of the carbons in the six-membered ring have one unhybridized p atomic orbital. All six of the unhybridized p orbitals overlap side to side to give a ring of electron density above and below the six- membered ring of benzene.

The six  electrons in the  bonds in benzene can roam about above and below the entire ring surface; these  electrons are delocalized. This is important because all six carbon-carbon bonds in benzene are equivalent in length and strength. The Lewis structures say something different (three of the bonds are single and three of the bonds are double). This is not correct.To explain the equivalent bonds, the  bonds can’t be situated between two carbon atoms as is the case in alkenes and alkynes; that is, the  bonds can’t be localized. Instead, the six  electrons can roam about over a much larger area; they are delocalized over the entire surface of the molecule. All this is implied in the following shorthand notation for benzene.

• A short summary of the nomenclature rules for alkanes, alkenes, and alkynes follows. See the

text for details.

• Memorize the base names of C1–C10 carbon chains (see Table 22.1). When the C1–C10

carbon chains are named as a substituent, change the –ane suffix to–yl.

• Memorize the additional substituent groups in Table 22.2.

• Names are based on the longest continuous carbon chain in the molecule. Alkanes use the

suffix –ane, alkenes end in –ene, and alkynes end in –yne.

• To indicate the position of a branch or substituent, number the longest chain of carbons

consecutively to give the lowest numbers to the substituents or branches. Identify the number of the carbon that the substituent is bonded to by writing the number in front of the name of the substituent.

• Name substituents in alphabetical order.

• Use a prefix (di–, tri–, tetra–, etc.) to indicate the number of a substituent if more than one

is present. Note that if, for example, three methyl substituent groups are bonded to carbons on the longest chain, use the tri-prefix but also include three numbers indicating the positions of the methyl groups on the longest chain. Also note that prefixes like di–, tri–, tetra–, etc. are not considered when determining the alphabetical order of the substituent groups.

• A cyclic hydrocarbon is designated by the prefix cyclo–.
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