4. Alkanes and Cycloalkanes

Draw a potential-energy diagram for rotation about the C-2---C-3 bond of pentane through 360°, starting with the least stable conformer.

Draw Newman projections of the following molecules viewed from the direction of the blue arrows.

(b)

Using Newman projections, draw the most stable conformer for each of the following:

b. 3-methylhexane, viewed along the C-3----C-4 bond

Which Newman projection best represents the most stable conformation of $C_2{H}_6$ (ethane) when viewed down the carbon-carbon bond?

Using the Newman projections shown, draw each molecule in its line-angle drawing with all hydrogens and substituents shown. [Carbon b is behind carbon a in these structures.] Wedges and dashes should be used to indicate whether a substituent is coming out of, or going into, the plane of the page.

(d)

Draw all the staggered and eclipsed conformers that result from rotation about the C-2-C-3 bond of pentane.

Convert each Newman projection to the equivalent line–angle formula, and assign the IUPAC name.

(c)

(d)

Using Newman projections, draw the most stable conformer for each of the following:

a. 3-methylpentane, viewed along the C-2---C-3 bond

Use a Newman projection about the indicated bond to draw the most stable conformer for each compound.

a. 3-methylpentane about the C2―C3 bond

Which of the following Newman projections best represents the most stable conformation of $C_2{H}_6$ (ethane) when viewed down the $C-C$ bond?

Which of the following Newman projections best represents the most stable conformation of $C_2{H}_6$ (ethane) when viewed down the $C-C$ bond?

Which of the following Newman projections correctly represents the staggered conformation of $C_2{H}_6$ (ethane) when viewed down the $C–C$ bond?

Given the following structures, show the Newman projection that would result from looking down the indicated bond in the direction shown. [Orient yourself as if you were the eyeball looking down the bond. Some of the examples have been partially completed for you to fill in the rest.]

(b) <IMAGE>

Conformational studies on ethane-1,2-diol (HOCH₂–CH₂OH) have shown the most stable conformation about the ­central C―C bond to be the gauche conformation, which is 9.6 kJ/mol (2.3 kcal/mol) more stable than the anti conformation. Draw Newman projections of these conformers, and explain this curious result.