Chapter 2 Flashcards
Alkanes are _______ hydrocarbons.
saturated
Alkenes are _______ hydrocarbons.
unsaturated
Alkynes are _______ hydrocarbons.
unsaturated
Arenes are _______ hydrocarbons.
unsaturated
Saturated hydrocarbons:
Contain only carbon-carbon single bonds
Unsaturated hydrocarbons
Contain one or more carbon-carbon double bond, triple bond, or benzene ring.
Alkane general molecular formula
C(n)H(2n+2)
Constitutional isomers
Have the same molecular formula but different atom connectivity.
Different constitutional isomers have:
different physical properties
Alkyl group
A substituent group derived from an alkane by the removal of a hydrogen atom
-e
hydrocarbon
-ol
alcohol
-al
aldehyde
-amine
amine
-one
ketone
-oic acid
carboxylic acid
Cycloalkane
A saturated hydrocarbon that contains atoms bonded to form a ring
Cyclic hydrocarbon
A hydrocarbon that contains carbon atoms joined to form a ring
Cycloalkane molecular formula:
C(n)H(2n)
If there are two substituents on a cycloalkane:
number the ring beginning with the substituent of lower alphabetic order.
If there are three or more substituents:
number the ring to give substituted carbons the lowest numbers (sum)
sec-
Indicates that a functional group is bonded to a secondary carbon atom in a chain of four or more carbon atoms
tert-
Indicates that a functional group is attached to a tertiary carbon atom.
iso-
Used to indicate that all carbons in a molecule are in a continuous chain, except one carbon that is part of an isopropyl group at the end of the chain.
Bicycloalkane
An alkane that consists of two rings that share two carbon atoms
Bridgehead carbons
The shared carbons in a bicycloalkane
Bicycloalkane formula
C(n)H(2n-2)
Staggered conformation
A conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from atoms or groups on an adjacent carbon atom.
Eclipsed conformation
A conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as close as possible to the atoms or groups on an adjacent carbon.
Torsional strain
Strain that arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation. Torsional strain is also called eclipsed-interaction strain.
Eclipsed conformations have ______ energy.
higher
Anti conformation
A conformation about a single bond in which two groups on adjacent carbons lie at a dihedral angle of 180.
Gauche conformation
A conformation about a single bond of an alkane in which two groups on adjacent carbons lie at a dihedral angle of 60.
Gauche and anti conformations are ______ conformations.
staggered
Steric strain
The strain that arises when nonbonded atoms separated by four or more bonds are forced closer to each other than their atomic (contact) radii would allow. Steric strain is also called nonbonded interaction strain, or van der Waals strain.
Small ring strain
A strain associated with ring sizes below six that arises from nonoptimal bond angles.
The observed C-C-C bond angles in cyclopropane:
60
How does puckering a ring alter the strain energy?
1) It decreases the torsional strain associated with eclipsed interactions
2) increases further the angle strain caused by the compression of C-C-C bond angles
Chair conformation
The most stable nonplanar conformation of a cyclohexane; all bond angles are 110.9, close to the optimum. All bonds on adjacent carbons are staggered.
Axial bonds
Perpendicular bonds
Equatorial bonds
Lies roughly along the equator of the ring
Diaxial interaction
The steric strain arising from interaction between an axial substituent and an axial hydrogen on the same side of the chair conformation.
Which is more stable, axial or equatorial substituents?
Equatorial
Stereoisomers
Compounds that have the same molecular formula and the same connectivity, but different orientation in space.
Stereocenter
An atom (most commonly a carbon atom) about which exchange of two groups produces a different stereoisomer.
Cis, trans isomers
Have the same molecular formula and same connectivity of atoms, but the arrangement of their atoms in space cannot be interconverted by rotation about single bonds.
Cis
substituents are on the same side of the ring
Trans
substituents are on opposite sides of the ring
Which is more stable, cis or trans isomers?
Trans
What intermolecular force do cycloalkanes contain?
dispersion forces
The strength of dispersion forces tend to increase with:
increasing molecular mass and size
Boiling points of alkanes are:
low
As the number of atoms and molecular weight of alkanes increase, the boiling point ______.
increases
Alkanes containing 1 to 4 carbons are _____ at room temperature.
gases
Alkanes containing 5 to 17 carbons are ________ at room temperature.
colorless liquids
Alkanes containing 18 or more carbons are ______ at room temperature.
white, waxy solids
Constitutional isomers are ______ compounds.
different
As the branching of an alkane increases, boiling point ______.
increases
Oxidation of alkanes
Oxidation of alkanes to carbon dioxide and water is the basis for their use as energy sources of heat and power.
In hydrocarbon oxidations, the energy of the products is ______ than that of the reactants.
less
Heat of combustion
The energy of the products minus that of the reactants
Longer straight-chained alkanes have a _____ melting point than shorter straight-chained alkanes.
higher
The density of an alkane _____ with increasing molecular weight.
increases
Branched alkanes are _____ stable than straight-chained alkanes.
more
Branched alkanes have a ____ boiling point than straight-chained alkanes.
lower
