Ch. 4 - Alkanes and CycloalkanesWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

We use Newman projections to visualize the rotations of conformers. Some are more stable than others. Let's take a look.

Concept #1: How sigma bond rotation is visualized

So Newman projections are way of analyzing which sigma bond rotation will be the most stable. We have some rules about which rotations are better and which are worse!

Three Types of Conformations

The dihedral angle (theta), is equal to the angle between the two largest groups on either side of the projection.

Concept #2: The energy states of 3 different Newman Projections.

Plotting a Newman Energy Diagram

As you’ll see, when we plot (theta) against energy, we wind up getting a predictable pattern of peaks and valleys that can be used to better understand the different rotations. 

Concept #3: How to draw a Newman Projection Energy Diagram.

Professors may ask you to draw this, so don’t just tune it out! You need to understand the basics of energy diagrams for this topic. 

Additional Problems
Circle the only Newman projection with a gauche interaction between the two methyl groups:
The eclipsed and staggered forms of butane are said to differ in:      (1) molecular formula      (2) configuration      (3) conformation       (4) constitution      (5) structure
The following chart describes the relationship between potential energy and torsional angle in butane (the torsional angle being measured about the C2-C3 bond). Identify the labeled maxima or minima as representing fully eclipsed, gauche or anti conformer energies. NOTE: "anti" or "trans" have the same definition: the groups are away from each other at a 180° angle.
(a) Write Newman projections for the gauche and anti conformations of 1,2- dichloroethane (ClCH2CH2Cl). 
Sketch an energy diagram that shows a conformational analysis of 2,2-dimethylpropane. Does the shape of this energy diagram more closely resemble the shape of the energy diagram for ethane or for butane?
What are the relative energy levels of the three staggered conformations of 2,3-dimethylbutane when looking down the C2—C3 bond?
Draw a relative energy diagram showing a conformational analysis of 1,2-dichloroethane. Clearly label all staggered conformations and all eclipsed conformations with the corresponding Newman projections.
Sketch curves similar to the one given in Fig. 4.8 showing the energy changes that arise from rotation about the C2 — C3 bond of (a) 2,3-dimethylbutane. You need not concern yourself with actual numerical values of the energy changes, but you should label all maxima and minima with the appropriate conformations.    
Sketch curves similar to the one given in Fig. 4.8 showing the energy changes that arise from rotation about the C2 — C3 bond of (b) 2,2,3,3-tetramethylbutane. You need not concern yourself with actual numerical values of the energy changes, but you should label all maxima and minima with the appropriate conformations.    
Which is 2-chloro-3-methylbutane?
Rank the following conformations in order of increasing energy:
Draw all conformations, using Newman projections, of 1,1,1-tribromo-2,2,2-trichloroethane. Label each using labels such as staggered, eclipsed, anti, or gauche.
A. Sketch the curve showing the energy changes that arise from rotation about the C2-C3 bond of 2,2-dimethylpropane. B. Label the axes of your graph. C. Draw and label (i.e., anti, staggered, eclipsed, or gauche) the Newman projections for each conformation.
Which Newman projection represents the most stable conformation of (CH3)2CHCH(CH3)2 ?
Complete the Newman projections for the most and least stable conformations looking along α to β.
A biosynthetic pathway was recently proposed for the polycyclic, cytotoxic compound aspernomine, isolated from the fungus Aspergillus nomius (J. Am. Chem. Soc. 2012, 134, 8078–8081): (b) What is the approximate dihedral angle between the two methyl  groups directly bound to the chairs?
What is the order from most stable to least stable for these conformations of propylene glycol? a) III > II > I b) I > II > III c) I > III > II d) II > III > I
The conformations of (+)-epichlorohydrin (1), viewed along the Ca—Cb bond, can be analyzed in exactly the same manner as the acyclic alkanes discussed in Chapter 4 (J. Phys. Chem. A 2000, 104, 6189–6196). (b) Identify the least stable staggered conformation for  1.
The conformations of (+)-epichlorohydrin ( 1), viewed along the Ca—Cb bond, can be analyzed in exactly the same manner as the acyclic alkanes discussed in Chapter 4 (J. Phys. Chem. A 2000, 104, 6189–6196). (c) The most stable conformation of 1,2-dichloropropane exhibits a methyl group that is anti to a chlorine atom. Using this information, identify the most stable conformation of 1 and justify your choice.
Draw the three lowest energy conformations of 3-methylpentane sighting down the C2-C3 bond in order of increasing energy (i.e. most to least stable).
Which Newman projection corresponds to point A on the graph of potential energy vs. rotation about the C2—C3 bond?
Draw the most stable Newman projection for each of the following compounds. a) 3-methylpentane (Looking down the C2-C3 bond)           b) 2,3-dimethylbutane (Looking down the C2-C3 bond)            
Draw the most stable Newman projection for the following compound
Sketch an energy diagram that shows a conformational analysis of 2,2-dimethylpropane. Does its energy diagram resemble the one for ethane or butane? 
For the pair of molecules drawn below, choose the letter that corresponds to the  MORE STABLE molecule. Does the UNSTABLE molecule chosen below have ANGLE STRAIN? Does the UNSTABLE molecule chosen below have TORSIONAL STRAIN? Does the UNSTABLE molecule chosen below have STERIC STRAIN?
For the pair of molecules drawn below, choose the letter that corresponds to the MORE STABLE molecule. Does the UNSTABLE molecule chosen have ANGLE STRAIN? (YES or NO) Does the UNSTABLE molecule chosen have TORSIONAL STRAIN? (YES or NO) Does the UNSTABLE molecule chosen have STERIC STRAIN? (YES or NO)
Conformational analysis is the study of the energy changes (stability) of different spatial arrangements of atoms relative to rotations about single bonds. Perform the following analyses: Using Newman Projections, fill in the potential energy diagram for the rotation around the C2-C3 bond in butane (i.e. draw each Newman Projection onto the diagram at each angle of rotation specified). ]
Sight down the C-2—C-3 bond, and draw Newman projection formulas for the  (b) Two most stable conformations of 2-methylbutane  
Sight down the C-2—C-3 bond, and draw Newman projection formulas for the  (c) Two most stable conformations of 2,3-dimethylbutane 
Rank the following molecule in order of increasing stability (least stable to most stable) A) 4, 1, 2, 3 B) 1, 2, 3, 4 C) 2, 3, 1, 4 D) 3, 2, 4, 1 E) 3, 2, 1, 4
One of the staggered conformations of 2-methylbutane in Problem 3.21b is more stable than the other. Which one is more stable? Why? 
Identify all atoms that are (a) anti and (b) gauche to bromine in the conformation shown for CH3CH2CH2Br.