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Chapter 4: Organic Compounds: Cycloalkanes and Their Stereoc
Part of OCHEM Test 1
94
Organic Chemistry
Undergraduate 2
06/05/2017
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Term
the general formula for cycloalkanes that have 1 ring
 Definition
CnH2n
Term
how to name cycloalkanes
 Definition
1: find the parent
2: number the substituents
Term
how to find the parent in a cycloalkane
 Definition
-if the number of C atoms in a ring is larger than the number in the largest substituent, the compound is named as an alkyl-substituted cycloalkane
-if the number of C atoms in the ring is smaller than the number in the largest substituent, the compound is named as a cycloalkyl-substituted alkane
Term
alkyl-substituted cycloalkane
 Definition
cycloalkane where the # of C atoms in the ring is larger than the number in the largest substituent
Term
cycloalkyl-substituted alkane
 Definition
cycloalkane where the # of C atoms in the ring is smaller than the number in the largest substituent
Term
how to number the substituents in a cycloalkane
 Definition
1: start at a point of attachment and number the substituents so that the second substituent has the lowest possible number
2: if necessary, proceed until a point of difference is found
3: if 2 or more substituents might potentially receive the same number, number them by alphabetical priority
4: halogens are treated in the same way as alkyl groups
Term
size of a cycloalkane's ring vs. amount of rotational freedom
 Definition
directly proportional
Term
cis-disubstituted cycloalkane ring
 Definition
has 2 substituents on the same side of the ring
Term
trans-disubstituted cycloalkane ring
 Definition
has 2 substituents on opposite sides of the ring
Term
general principles of conformation of cycloalkanes
 Definition
1: ring strain
2: heats of combustion of cycloalkanes
3: the nature of ring strain
Term
how to measure the strain in cycloalkanes
 Definition
measure the total energy of a compound and compare it to a strain-free reference compound
Term
heat of combustion
 Definition
the amount of heat released when a compound is completely burned in oxygen
Term
amount of strain vs. heat of combustion
 Definition
directly proportional
Term
how strain a per CJH2 unit can be calculated and plotted
 Definition
as a function of ring size
Term
the rings that have serious strain
 Definition
small rings
Term
rings tend to adopt these conformations
 Definition
puckered
Term
factors that account for ring strain
 Definition
-angle strain occurs when bond angles are distorted from their normal values
-torsional strain is due to eclipsing of bonds
-steric strain results when atoms approach too closely
Term
angle strain
 Definition
occurs when bond angles are distorted from their normal values
Term
torsional strain
 Definition
caused by eclipsing of bonds
Term
steric strain
 Definition
results when atoms approach too closely
Term
some small cycloalkane rings
 Definition
-cyclopropane
-cyclobutane
-cyclopentane
Term
why cyclopropane is more reactive than other cycloalkanes
 Definition
because of bent bonds
Term
what cyclopentane does to relieve torsional strain
 Definition
adopts a puckered conformation
Term
puckered conformation
 Definition
in this conformation, one C is bent out of plane and the H's are nearly staggered
Term
a conformation of cyclohexane
 Definition
chair cyclohexane
Term
where the bonds are in chair conformation cyclohexane
 Definition
lower bonds in front and upper bonds in back
Term
the strain in chair conformation cyclohexane
 Definition
no strain
Term
the strain that results when chair conformation cyclohexane converts to boat conformation cyclohexane
 Definition
has little ange strain, but experiences both steric and torsional strain
Term
the 2 kinds of positions on a cyclohexane ring
 Definition
-6 axial H's
-6 equatorial H's
Term
axial H's
 Definition
perpendicular to the plane of the ring
Term
equatorial H's
 Definition
roughly in the same plane of the ring
Term
the orientation of the H's of each C in cyclohexane
 Definition
each C has 1 axial H and 1 equatorial H
Term
orientation of the H's on the side of the ring in cyclohexane
 Definition
each side of the ring has alternating axial and equatorial H's
Term
if all the H's in a cyclohexane ring are on the same face, they are...
 Definition
cis
Term
how different chair conformations of cyclohexanes interconvert
 Definition
by a ring flip
Term
what a ring flip does to the axial and equatorial bonds in cyclohexane
 Definition
an axial bond becomes equatorial and an equatorial bond becomes axial
Term
the energy barrier to conversion in cyclohexane
 Definition
45 kJ/mol
Term
diaxial interactions
 Definition
interactions between an axial group and a ring H 2 C's away
Term
what causes diaxial interactions?
 Definition
steric strain
Term
the interactions that occur in gauche butane
 Definition
diaxial interactions caused by steric energy
Term
the position in which substituents on a cycloalkane are more stable
 Definition
equatorial position
Term
the size of the strain between substituents in a cyclohexane depends on...
 Definition
the size and nature of the group
Term
the orientation of the substituents in the chair conformations of a cis isomer
 Definition
one is axial and the other is equatorial
Term
the orientation of the substituents in the chair conformations of a trans isomer
 Definition
both are either axial or equatorial
Term
why axial orientation is less stable than equatorial orientation
 Definition
because there's diaxial interactions in the axial orientation
Term
2 ways cycloalkane rings can be fused
 Definition
-cis-fused
-trans-fused
Term
bicyclic ring systems
 Definition
have rings that are connected by bridges
Term
the general formula for cycloalkanes that have 1 ring
 Definition
CnH2n
Term
how to name cycloalkanes
 Definition
1: find the parent
2: number the substituents
Term
how to find the parent in a cycloalkane
 Definition
-if the number of C atoms in a ring is larger than the number in the largest substituent, the compound is named as an alkyl-substituted cycloalkane
-if the number of C atoms in the ring is smaller than the number in the largest substituent, the compound is named as a cycloalkyl-substituted alkane
Term
alkyl-substituted cycloalkane
 Definition
cycloalkane where the # of C atoms in the ring is larger than the number in the largest substituent
Term
cycloalkyl-substituted alkane
 Definition
cycloalkane where the # of C atoms in the ring is smaller than the number in the largest substituent
Term
how to number the substituents in a cycloalkane
 Definition
1: start at a point of attachment and number the substituents so that the second substituent has the lowest possible number
2: if necessary, proceed until a point of difference is found
3: if 2 or more substituents might potentially receive the same number, number them by alphabetical priority
4: halogens are treated in the same way as alkyl groups
Term
size of a cycloalkane's ring vs. amount of rotational freedom
 Definition
directly proportional
Term
cis-disubstituted cycloalkane ring
 Definition
has 2 substituents on the same side of the ring
Term
trans-disubstituted cycloalkane ring
 Definition
has 2 substituents on opposite sides of the ring
Term
general principles of conformation of cycloalkanes
 Definition
1: ring strain
2: heats of combustion of cycloalkanes
3: the nature of ring strain
Term
how to measure the strain in cycloalkanes
 Definition
measure the total energy of a compound and compare it to a strain-free reference compound
Term
heat of combustion
 Definition
the amount of heat released when a compound is completely burned in oxygen
Term
amount of strain vs. heat of combustion
 Definition
directly proportional
Term
how strain a per CJH2 unit can be calculated and plotted
 Definition
as a function of ring size
Term
the rings that have serious strain
 Definition
small rings
Term
rings tend to adopt these conformations
 Definition
puckered
Term
factors that account for ring strain
 Definition
-angle strain occurs when bond angles are distorted from their normal values
-torsional strain is due to eclipsing of bonds
-steric strain results when atoms approach too closely
Term
angle strain
 Definition
occurs when bond angles are distorted from their normal values
Term
torsional strain
 Definition
caused by eclipsing of bonds
Term
steric strain
 Definition
results when atoms approach too closely
Term
some small cycloalkane rings
 Definition
-cyclopropane
-cyclobutane
-cyclopentane
Term
why cyclopropane is more reactive than other cycloalkanes
 Definition
because of bent bonds
Term
what cyclopentane does to relieve torsional strain
 Definition
adopts a puckered conformation
Term
puckered conformation
 Definition
in this conformation, one C is bent out of plane and the H's are nearly staggered
Term
a conformation of cyclohexane
 Definition
chair cyclohexane
Term
where the bonds are in chair conformation cyclohexane
 Definition
lower bonds in front and upper bonds in back
Term
the strain in chair conformation cyclohexane
 Definition
no strain
Term
the strain that results when chair conformation cyclohexane converts to boat conformation cyclohexane
 Definition
has little ange strain, but experiences both steric and torsional strain
Term
the 2 kinds of positions on a cyclohexane ring
 Definition
-6 axial H's
-6 equatorial H's
Term
axial H's
 Definition
perpendicular to the plane of the ring
Term
equatorial H's
 Definition
roughly in the same plane of the ring
Term
the orientation of the H's of each C in cyclohexane
 Definition
each C has 1 axial H and 1 equatorial H
Term
orientation of the H's on the side of the ring in cyclohexane
 Definition
each side of the ring has alternating axial and equatorial H's
Term
if all the H's in a cyclohexane ring are on the same face, they are...
 Definition
cis
Term
how different chair conformations of cyclohexanes interconvert
 Definition
by a ring flip
Term
what a ring flip does to the axial and equatorial bonds in cyclohexane
 Definition
an axial bond becomes equatorial and an equatorial bond becomes axial
Term
the energy barrier to conversion in cyclohexane
 Definition
45 kJ/mol
Term
diaxial interactions
 Definition
interactions between an axial group and a ring H 2 C's away
Term
what causes diaxial interactions?
 Definition
steric strain
Term
the interactions that occur in gauche butane
 Definition
diaxial interactions caused by steric energy
Term
the position in which substituents on a cycloalkane are more stable
 Definition
equatorial position
Term
the size of the strain between substituents in a cyclohexane depends on...
 Definition
the size and nature of the group
Term
the orientation of the substituents in the chair conformations of a cis isomer
 Definition
one is axial and the other is equatorial
Term
the orientation of the substituents in the chair conformations of a trans isomer
 Definition
both are either axial or equatorial
Term
why axial orientation is less stable than equatorial orientation
 Definition
because there's diaxial interactions in the axial orientation
Term
2 ways cycloalkane rings can be fused
 Definition
-cis-fused
-trans-fused
Term
bicyclic ring systems
 Definition
have rings that are connected by bridges
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