Chapter 2.5: Conformations of Alkane and Cycloalkanes

Question 1

What is any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond?

Answer 1

conformation

Question 2

What type of strain is common in the eclipsed conformation?

Answer 2

torsional strain

Question 3

Define strain

Answer 3

an instability within a structure associated with higher internal energy

Question 4

Define gauche conformation

Answer 4

a conformation about a single bond of alkane in which two groups on adjacent carbons lie at a dihedral angle of 60°

Question 5

What is the strain that arises when a bond angle is either compressed or expanded compared to its optimal value?

Answer 5

angle strain

Question 6

What is 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 non-bonded interaction strain, or van der Waals strain.?

Answer 6

steric strain

Question 7

Define chair conformation

Answer 7

the most stable nonplanar conformation of a cyclohexane ring; all bond angles are ~109.5°, and all bonds on adjacent carbons are staggered

Question 8

What is a conformation about a carbon-carbon single bond in which atoms or groups on one carbon are as far apart as possible from atoms or groups on an adjacent carbon?

Answer 8

staggered conformation

Question 9

What is the most stable nonplanar conformation of a cyclohexane ring; all bond angles are ~109.5°, and all bonds on adjacent carbons are staggered?

Answer 9

chair conformation

Question 10

What is a bond to a chair conformation of cyclohexane that extends from the ring roughly perpendicular to the imaginary axis through the center of the ring, a bond that lies roughly along the equator of a cyclohexane ring?

Answer 10

equatorial bonds

Question 11

What is a conformation about a single bond of alkane in which two groups on adjacent carbons lie at a dihedral angle of 60°?

Answer 11

gauche conformation

Question 12

Define eclipsed conformation

Answer 12

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

Question 13

Define torsional strain

Answer 13

strain that arises when nonbonded atoms separated by 3 bonds are forced from a staggered conformation to an eclipsed conformation. Also called eclipsed-interaction strain.

Question 14

Define equatorial bonds

Answer 14

a bond to a chair conformation of cyclohexane that extends from the ring roughly perpendicular to the imaginary axis through the center of the ring, a bond that lies roughly along the equator of a cyclohexane ring

Question 15

Define angle strain

Answer 15

the strain that arises when a bond angle is either compressed or expanded compared to its optimal value

Question 16

What is a nonplanar conformation of a cyclohexane ring that is twisted from and slightly more stable than a boat conformation?

Answer 16

twist-boat

Question 17

Define anticonformation

Answer 17

a conformation about a single bond of alkane in which two groups on adjacent carbons lie at the dihedral angle of 180°

Question 18

Define steric strain

Answer 18

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 non-bonded interaction strain, or van der Waals strain.

Question 19

What is the angle created by two interesting planes?

Answer 19

dihedral angle (θ)

Question 20

How is steric strain produced in a chair conformation?

Answer 20

 Any group larger than an H atom will experience steric strain if it is axial

Question 21

What is a conformation about a single bond of alkane in which two groups on adjacent carbons lie at the dihedral angle of 180°?

Answer 21

anticonformation

Question 22

Define diaxial (axial-axial) interaction

Answer 22

refers to steric strain arising from interaction between an axial hydrogen (or other groups) on the same side of a chair conformation of a cyclohexane ring

Question 23

Define dihedral angle (θ)

Answer 23

the angle created by two interesting planes

Question 24

What is an instability within a structure associated with higher internal energy?

Answer 24

strain

Question 25

What is a strain associated with ring sizes below six that arises from nonoptimal bond angles?

Answer 25

small ring strain

Question 26

What is 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?

Answer 26

eclipsed conformation

Question 27

Define Newman projection

Answer 27

a way to view a molecule by looking along a carbon-carbon single bond

Question 28

What refers to steric strain arising from interaction between an axial hydrogen (or other groups) on the same side of a chair conformation of a cyclohexane ring?

Answer 28

diaxial (axial-axial) interaction

Question 29

What is a way to view a molecule by looking along a carbon-carbon single bond?

Answer 29

Newman projection

Question 30

Define staggered conformation

Answer 30

a conformation about a carbon-carbon single bond in which atoms or groups on one carbon are as far apart as possible from atoms or groups on an adjacent carbon

Question 31

Define axial bonds

Answer 31

a bond to a chair conformation of cyclohexane that extends from the ring parallel to the imaginary axis through the center of the ring; a bond that lies roughly perpendicular to the equator of the ring

Question 32

Define twist-boat

Answer 32

a nonplanar conformation of a cyclohexane ring that is twisted from and slightly more stable than a boat conformation

Question 33

Define small ring strain

Answer 33

a strain associated with ring sizes below six that arises from nonoptimal bond angles

Question 34

What is a nonplanar conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other?

Answer 34

boat

Question 35

What is strain that arises when nonbonded atoms separated by 3 bonds are forced from a staggered conformation to an eclipsed conformation. Also called eclipsed-interaction strain.?

Answer 35

torsional strain

Question 36

Define conformation

Answer 36

any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond

Question 37

Define boat

Answer 37

a nonplanar conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other

Question 38

What is a bond to a chair conformation of cyclohexane that extends from the ring parallel to the imaginary axis through the center of the ring; a bond that lies roughly perpendicular to the equator of the ring?

Answer 38

axial bonds

Question 39

What is present in a staggered conformation that helps reduce torsional strain?

Answer 39

 Hyperconjugation helps reduce torsional strain

Question 40

How can alkanes of 2 or more carbons be twisted?

Answer 40

o Alkanes of two or more carbons can be twisted into a number of different 3-dimensional arrangements of their atoms by rotating about one or more carbon-carbon bonds