Chapter 11,12,13 chemistry

Cycloalkanes with substituents on two or more carbons of the ring show a type of isomerism called cis-trans isomerism.
what is Cis-Trans Isomerism in Cycloalkanes
isomers that have the same connectivity of their atoms but a different arrangement of their atoms in space due to the presence of either a ring or a carbon-carbon double bond.
Cis-trans isomers
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an atom or group of atoms within a molecule that shows a characteristic set of predictable physical and chemical behaviours
functional group
true
A hydrocarbon is composed only of the elements carbon and hydrogen.
true
Alkanes are saturated hydrocarbons
true
The general formula of an alkane is CnH2n+2, where n is the number of carbons in the alkane
true
Alkenes and alkynes are unsaturated hydrocarbons
compound that contains only hydrogen and carbon
hydrocarbon
saturated hydrocarbon
alkane
hydrocarbon that only carbon – carbon single
saturated hydrocarbon bonds
The carbon chain of an alkane is not straight; it is bent with all C-C-C bond angles of approximately 109.5°.
Why is it not accurate to describe an unbranched alkane as a “straight-chain” hydrocarbon
Each line terminus and vertex represents a carbon atom. Single, double, and triple carbon-carbon bonds are represented
by one, two, and three lines, respectively.
What is meant by the term line-angle formula as applied to alkanes and cycloalkanes?
false
Constitutional isomers have the same molecular formulas and the same connectivity of their atoms
false
There are two constitutional isomers with the molecular formula C3H8.
false
There are four constitutional isomers with the molecular formula C4H10
false
There are five constitutional isomers with the molecular formula C5H12.
a. They have the same molecular formula True

b. They have the same molecular weight. True

c. They have the same connectivity of their atoms. False

d. They have the same physical properties

Which statements are true about constitutional isomers
true
The parent name of an alkane is the name of the longest chain of carbon atoms in the alkane
true
Propyl and isopropyl groups are constitutional isomers.
true
ethyl
isobutyl
isopropyl
tert-butyl (t-butyl)
There are four alkyl groups with the molecular formula C4H9.
true
Cycloalkanes are saturated hydrocarbons
false
Hexane and cyclohexane are constitutional isomers
false
The parent name of a cycloalkane is the name of the unbranched alkane with the same number of carbon atoms
as are in the cycloalkane ring.
false
. Conformations have the same molecular formula and the same connectivity but differ in the three-dimensional
arrangement of their atoms in space
true
In all conformations of ethane, propane, butane, and higher alkanes, all C – C – C and H – C – H bond angles
are approximately 109.5oC
true
In a cyclohexane ring, if an axial bond is above the plane of the ring on a particular carbon, axial bonds on the
two adjacent carbons are below the plane of the ring
true
In a cyclohexane ring, if an equatorial bond is above the plane of the ring on a particular carbon, equatorial
bonds on the two adjacent carbons are below the plane of the ring
true
The more stable chair conformation of a cyclohexane ring has more substituent groups in equatorial positions
false
Cis- and trans- cycloalkanes have the same molecular formula but a different connectivity of their atoms.
false
A cis isomer of a cycloalkane can be converted to its trans isomer by rotation about an appropriate
carbon-carbon single bond
true
. A cis isomer of a cycloalkane can be converted to its trans isomer by exchange of two groups at a stereocenter
in the cis-cycloalkane
true
Configuration refers to the arrangement in space of the atoms or groups of atoms at a stereocenter
false
Cis-1,4-dimethylcyclohexane and trans-1,4-dimethylcyclohexane are classified as conformations.
true
Boiling points among alkanes with unbranched chains increase as the number of carbons in the chain increases
true
Alkanes and cycloalkanes are insoluble in water
true
Liquid alkanes are soluble in each other.
All liquid alkanes are less dense than water
What generalizations can you make about the densities of alkanes relative to the density of water
Both hexane and octane are colorless liquids, so you could not tell which is which simply by looking at them. To tell the
two liquids apart, you would need to measure some physical property in which they differ such as boiling point.
Suppose that you have samples of hexane and octane. Could you tell the difference by looking at them? What color would each
be? How could you tell which is which?
false
Combustion of alkanes is an endothermic reaction
true
The products of complete combustion of an alkane are carbon dioxide and water
true
Halogenation of an alkane converts it to a haloalkane.
false
Both ethylene and acetylene are planar molecules.
true
An alkene in which each carbon of the double bond has two different groups bonded to it will show
cis-trans isomerism.
false
Cis-trans isomers have the same molecular formula but a different connectivity of their atoms.
false
Cis-2-butene and trans-2-butene can be interconverted by rotation about the carbon-carbon
double bond.
true
Cis-trans isomerism is possible only among approximately substituted alkenes.
true
Both 2-hexene and 3-hexene can exist as pairs of cis-trans isomers.
false
Cyclohexene can exist as a pair of cis-trans isomers.
false
1-chloropropene can exist as a pair of cis-trans isomers.
A saturated hydrocarbon contains only carbon-carbon single bonds. An unsaturated hydrocarbon contains one or more
carbon-carbon double or triple bonds.
What is the difference in structure between a saturated hydrocarbon and an unsaturated hydrocarbon?
true
The IUPAC name of an alkene is derived from the name of the longest carbon chain that contains the
carbon-carbon double bond.
false
The IUPAC name of CH3CH=CHCH3 is 1,2-methylethene
false
2-methyl-2-butene shows cis-trans isomerism
true
e. The IUPAC name of CH2=CHCH=CHCH3 is 1,3-pentadiene.
The structural feature that makes cis-trans isomerism possible in alkenes is restricted rotation about the carbon-carbon double bond. In cycloalkanes, it is restricted rotation about the carbon-carbon bonds of the ring. These two structural features have in common restricted rotation about carbon-carbon bonds
What structural feature in alkenes make cis-trans isomerism in them possible? What structural feature in cycloalkanes makes
cis-trans isomerism in them possible? What do these two structural features have in common?
true
Alkenes and alkynes are nonpolar molecules
true
The physical properties of alkenes are similar to those of alkanes of the same carbon skeleton.
true
Alkenes that are liquid at room temperature are insoluble in water and when added to water, will float
on water.
true
Complete combustion of an alkene gives carbon dioxide and water.
true
Addition reactions of alkenes involve breaking one of the bonds of the carbon-carbon double bond
and formation of two new single bonds in its place
true
Markovnikov’s rule refers to the regioselectivity of additions reactions of carbon-carbon double bonds.
true
According to Markovnikov’s rule, hydrogen adds to the carbon of the double bond that already has the
greater number of hydrogen atoms bonded to it and the halogen adds to the carbon that has the lesser
number of hydrogen atoms bonded to it
false
A carbocation is a carbon atom with four bonds that bear a positive charge.
true
The carbocation derived from ethylene is CH3CH2+.
true
The reaction mechanism for the addition of a halogen acid (HX) to an alkene is divided into two steps,
(1) formation of a carbocation and (2) reaction of the carbocation with halide ion, which complete the reaction.
true
Acid-catalyzed addition of H2O to an alkene is called hydration.
true
If a compound fails to react with Br2, it is unlikely that the compound contains a carbon-carbon double bond.
true
Addition of H2 to a double bond is a reduction reaction
false
Catalytic reduction of cyclohexene gives hexane
false
. According to the mechanism presented in the text for acid-catalyzed hydration of an alkene, the H and
the -OH groups added to the carbon-carbon double bond both arise from the same molecule of H2O.
false
. The conversion of ethylene, CH2=CH2, to ethanol, CH3CH2OH, is an oxidation reaction.
true
Alkene, alkyne, and arenes are unsaturated hydrocarbons.
true
Aromatic compounds were so named because many of them have pleasant odors.
true
According to the resonance model of bonding, benzene is best described as a hybrid of two equivalent
contributing structures.
true
Benzene is a planar molecule.
A saturated compound contains only single covalent bonds. An unsaturated compound contains one or more double or
triple bonds. The most common types of double and triple bonds are:
C = C C = O C = N: – C C – – C N:
3. What is the difference in benzene structure between a saturated and an unsaturated compound?
An aromatic compound is one that contains one or more benzene rings.
Define aromatic compound.
Benzene consists of carbons, each surrounded by three regions of electron density, which gives 120° for all bond angles. Bond angles of 120° in benzene can be maintained only if the molecule is planar. Cyclohexane, on the other hand, consists of carbons, each surrounded by four regions of electron density, which gives 109.5° for all bond angles. Angles of 109.5° in cyclohexane can be maintained only if the molecule is nonplanar.
Account for the fact that the six-membered ring in benzene is planar but the six-membered ring in cyclohexane is not
true
a. A phenyl group has the molecular formula C6H5- and is represented by the symbol Ph- .
false
b. Para substituents occupy adjacent carbons on a benzene ring
Only cyclohexene will react with a solution of bromine in dichloromethane. A solution of Br2/CH2Cl2 is reddish-purple, whereas benzene and 1,2-dibromocyclohexane are both colorless. To tell which bottle contains which compound, place a small quantity of each compound in a test tube and to each test tube, add a few drops of Br2/CH2Cl2 solution. If the red color disappears, the compound is cyclohexene, which is converted to 1,2-dibromocyclohexane. If the reddish-purple color remains, the compound is benzene.
Suppose you have unlabeled bottles of benzene and cyclohexene. What chemical reaction could you use to tell which bottle
contains which chemical? Explain what you would do, what you would expect to see, and how you would explain your
observations. Write an equation for a positive test.
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