91影视

Consider separate 1.0-L samples of O₂(g) and He(g), both at 25^oC and the same pressure. Compare the change in momentum per impact and the number of impacts per second in the two samples.

Question: Locate the isoprene units in each compound.

Question: An isoprene unit can be thought of as having a head and a tail. The 鈥渉ead鈥� of the isoprene unit is located at the end of the chain nearest the branch point, and the 鈥渢ail鈥� is located at the end of the carbon chain farthest from the branch point. Most isoprene units are connected together in a 鈥渉ead-to-tail鈥� fashion, as illustrated. For both lycopene (Problem 31.26), and squalene (Figure 31.9), decide which isoprene units are connected in a head-to-tail fashion and which are not.

Question: Draw a stepwise mechanism for the conversion of neryl diphosphate to $\mathit{伪}\mathbf{-}\mathit{p}\mathit{i}\mathit{n}\mathit{e}\mathit{n}\mathit{e}$, $\mathit{伪}\mathbf{-}\mathit{p}\mathit{i}\mathit{n}\mathit{e}\mathit{n}\mathit{e}$is a component of pine oil and rosemary oil.

Locate the isoprene units in each compound.

a.

b.

c.

d.

Locate the isoprene units in each compound.

a.

b.

c.

d.

Draw the enantiomer and any two diastereomers of cholesterol. Does the OH group of cholesterol occupy an axial or equatorial position?

Treatment of cholesterol with mCPBA results in formation of a single epoxide A, with the stereochemistry drawn. Why isn鈥檛 the isomeric epoxide B formed to any extent?

Draw the products formed when triacylglycerol A is treated with each reagent. Rank compounds A, B and C in order of increasing melting point.

a.${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$,${\mathbf{H}}^{\mathbf{+}}$

b. ${\mathbf{H}}_{\mathbf{2}}$(excess), $\mathbf{Pd}\mathbf{.}\mathbf{C}\mathbf{鈫�}\mathbf{B}$

c.${\mathbf{H}}_{\mathbf{2}}$(1 equiv), $\mathbf{Pd}\mathbf{.}\mathbf{C}\mathbf{鈫�}\mathbf{C}$

Draw the products formed when cholesterol is treated with each reagent. Indicate the stereochemistry around any stereogenic centers in the product.

1. ${\mathbf{CH}}_{\mathbf{3}}\mathbf{COCl}$
   
2. ${\mathbf{H}}_{\mathbf{2}}\mathbf{,}\mathbf{}\mathbf{Pd}\mathbf{-}\mathbf{C}$
3. PCC
4. $\mathbf{oleic}\mathbf{}\mathbf{acid}\mathbf{,}\mathbf{}{\mathbf{H}}^{\mathbf{+}}$
5. $\left[1\right]{\mathbf{BH}}_{\mathbf{3}}\mathbf{路}\mathbf{THF}\mathbf{;}\left[2\right]{\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{2}}\mathbf{,}\mathbf{-}\mathbf{OH}$