Orgo smartbook Chapter 3

staggered eclipsed

-C-H bonds on one carbon bisect the H-C-H bond angles on the adjacent carbon. -C-H bonds on adjacent C atoms are aligned

An eclipsed conformation has a torsion angle of _____∘, gauche has a torsion angle of _____∘, and anti has a torsion angle of _____∘.

0; 60; 180

What is the name of the steric interactions between an axial substituent and other axial hydrogens/substituents on the same face of the cyclohexane chair conformation?

1,3-diaxial repulsions

The Newman projections for the conformers of 2-methylbutane, drawn from the perspective of the C2-C3 bond, are shown. Arrange these conformers in order of increasing energy (lowest energy at the top).

1. Structure B 2. Structure C 3. Structure D 4. Structure A

Rank the following conformations in order of increasing stability, starting with the less stable at the top of the list.

1. eclipsed 2. staggered

The Newman projections for the conformers of pentane, drawn from the perspective of the C2-C3 bond, are shown. Arrange these conformers in order of increasing stability (least stable at the top).

1. structure A 2. structure C 3. Structure D 4. structure B

How many different staggered conformations of butane can be drawn looking down the C2-C3 bond? Consider conformations with the same potential energy to be identical.

2

Ethane has a total of _____ conformations; _____ are eclipsed and _____ are staggered.

6; 3; 3

What is a heterocyclic compound?

A cyclic molecule with at least one noncarbon ring atom

Select all the statements that correctly define the terms cis and trans in relation to cycloalkanes.

A trans isomer has one "up" substituent and one "down" substituent. A cis isomer has two substituents on the same face of the ring.

Match the value of the dihedral angle to the conformations shown.

A= 60 B=0

Select all the statements that correctly describe the chair conformation of cyclohexane.

All hydrogen atoms on adjacent carbon atoms are staggered. The bond angles are near 109.50. Each carbon atom has one axial and one equatorial hydrogen atom.

What are the two orientations of hydrogen atoms in a cyclohexane chair?

Axial and equatorial

Select all of the possible orientations for the two substituents in a trans-1,2-disubstituted cyclohexane.

Axial-axial Equatorial-equatorial

Which ring system(s) shown is/are bridged bicyclic?

B

Select all the chair conformations that represent trans-1,3-dibromocyclohexane (shown).

B C

What is the IUPAC name for the molecule shown?

Bicyclo[2.2.2]octane

What is the IUPAC name for the molecule shown?

Bicyclo[3.2.0]heptane

An eclipsed conformation has a torsion angle of ∘, gauche has a torsion angle of ∘, and anti has a torsion angle of ∘.

Blank 1: 0 or zero Blank 2: 60 or sixty Blank 3: 180 or one hundred eighty

-1,4-dichlorocyclohexane can adopt a conformation with both of its substituents in equatorial positions, while an axial, equatorial conformation is the only possibility for -1,4-dichlorocyclohexane.

Blank 1: Trans or Trans- Blank 2: cis or cis-

An increase in energy caused by the deviation of tetrahedral bond angles from the optimum angle of 109.5° is called strain. This type of strain is found typically in - alkanes.

Blank 1: angle Blank 2: cyclo

The hydrogen atoms in the chair conformation of cyclohexane are divided into a set of six hydrogens and a set of six hydrogens.

Blank 1: axial Blank 2: equatorial

Trans-1,4-dibromocylohexane is more stable than the cis isomer because only the trans isomer can adopt a conformation in which both bromine atoms are in orientations.Trans-1,4-dibromocylohexane is more stable than the cis isomer because only the trans isomer can adopt a conformation in which both bromine atoms are in orientations.

Blank 1: equatorial

Two staggered Newman projections of butane are shown. In Structure A, the methyl groups have a(n) relationship; in Structure B, they are

Blank 1: gauche Blank 2: anti

A heterocycle is a cyclic molecule in which at least one of the atoms of the ring is a i.e., an atom of an element other than carbon.

Blank 1: heteroatom

Consider the two conformers of 1-fluoroethane. Conformer A is stable than conformer B, and the energy of conformer A is than the energy of conformer B.

Blank 1: less Blank 2: higher, greater, or more

Eclipsed conformations are stable than staggered conformations and the energy of an eclipsed conformation is than the energy of a staggered conformatio

Blank 1: less Blank 2: higher, greater, or more

Eclipsed conformations are stable than staggered conformations and the energy of an eclipsed conformation is than the energy of a staggered conformation.

Blank 1: less Blank 2: higher, greater, or more

Steric hindrance occurs in a molecule when the distance between two atoms in a given conformation is less than the sum of their van der Waals _________.

Blank 1: radii

Isomers that differ only in the way the atoms are oriented in space are called -isomers.

Blank 1: stereo

An increase in energy that results from atoms being forced too close to one another is called strain, while an increase in energy caused by eclipsing interactions is called strain.

Blank 1: steric or van der Waals Blank 2: torsional or eclipsing

For a cycloalkane, two groups that are on the opposite side of the ring are described as , whereas groups that are on the same side of the ring are described as .

Blank 1: trans Blank 2: cis

For any given cyclohexane molecule, there are possible chair conformations. A molecule moves between these conformations in a process known as ring .

Blank 1: two or 2 Blank 2: inversion, interconversion, flipping, or flip

Match each conformer of 1-chloroethane correctly according to relative stability.

Conformer A -> more stable Conformer B -> less stable

Which of the following rings has four conformations with similar energy?

Cycloheptane

Which of the molecules shown represent trans-1,4-dimethylcyclohexane (shown)? Select all that apply.

D B

Select the statement that correctly defines stereoisomers.

Isomers that differ only in the way their atoms are oriented in space

What is the name of the following spiro compound?

Spiro[2.2]pentane

Select the correct definition for steric strain.

Steric strain is an increase in energy caused by two or more atoms being forced too close to one another.

Which structure shown is the most stable conformation of bromocyclohexane?

Structure A

Select all the statements that correctly interpret the Newman projection shown.

The hydrogen marked "a" is on the back carbon atom. The Cl atom is attached to the front carbon atom.

Why is trans-1,4-diethylcyclohexane more stable than the cis isomer?

The trans isomer can adopt a conformation with both substituents in the less-sterically hindered equatorial orientation, while the cis isomer cannot.

Select all the statements that correctly describe the procedure for drawing a Newman projection. Assume the carbon atoms concerned have only single bonds and no nonzero formal charges.

There will be 3 bonds drawn for each C atom. A Newman projection considers one C-C bond at a time. A circle and a point are used to represent the two relevant C atoms.

Which of the following strains are predominant in the planar structure of cyclopentane?

Torsional strain

The most stable conformation for cyclohexane is the _____ conformation. In this conformation, _____ strain is eliminated because all internal bond angles are equal to 109.5°. All bonds to hydrogen atoms on adjacent carbon atoms are _____, and therefore torsional strain is minimized.

chair; angle; staggered

Match each stereoisomer of a 1,4-disubstituted cyclohexane to its possible substituent orientations.

cis-axial, equatorial or equatorial axial trans- axial, axial or equatorial, equatorial

The angle that separates a bond on one atom from a bond on an adjacent atom is called a Blank, angle. For a pair of eclipsed bonds (as in the conformation shown) the value of this angle is Blank 2 degree

dehedral 0

The electron-electron repulsion between electrons in σ bonds is at a maximum in the eclipsed conformation and these electron interactions are also known as _____ interactions. The increase in energy that results is called _____ strain.

eclipsing; torsional

For a monosubstituted cyclohexane, the most stable conformation is one that places the substituent in the ______ position.

equatorial

The structure on the left is _____ stable than the structure on the right because one methyl has _____ strain.

less; 1,3-diaxial

Consider a graph of energy versus dihedral angle for conformations of ethane. When the dihedral angle between any two hydrogens is 0°, the energy of the system is at a _____. As the dihedral angle increases, the energy of the system _____ until it reaches a ______ at a dihedral angle of 60°.

maximum, decreases, minimum

Consider a graph of energy versus dihedral angle for conformations of ethane. When the dihedral angle between any two hydrogens is 0°, the energy of the system is at a _____. As the dihedral angle increases, the energy of the system _____ until it reaches a ______ at a dihedral angle of 60°.

maximum; decreases; minimum

The three carbon atoms of cyclopropane all occupy the same .

plane

The following molecule is considered a _____ ring.

polycyclic

The strain caused by the small internal angles of cyclopropane and cyclobutane is known as strain.

ring

What is the orientation of the two substituents in the molecule shown?

sis

The most and least stable conformations of ethane are shown. Conformer A in which the C-H bonds on one carbon bisect the H-C-H bond angle on the adjacent carbon is called a(n) conformation. Conformer B is the conformation, in which the C-H bonds of one carbon are directly aligned with the C-H bonds on the adjacent carbon.

staggered, eclipsed

Destabilization that occurs in a molecule when two nonbonded atoms are too close together is called _____.

steric hindrance

The planar conformation of cyclopentane is unstable because its multiple eclipsed C-H bonds create significant strain.

torsional

The type of strain that results from repulsion between the electrons in eclipsed σ bonds is called _____ strain.

torsional

True or false: A cyclohexane ring can adopt two different chair conformations.

true

True or false: All of the carbon atoms of cyclopropane are in the same plane.

true

True or false: Conformational analysis of cycloheptane and higher cycloalkanes is complicated due to an increase in the number of atoms, bonds, and possible conformations.

true

A polycyclic compound contains at least connected rings.

two

In a bridged bicyclic ring system, atoms are common to at least two rings.

two