For each of the following compounds, indicate whether or not it can exist as cis–trans stereoisomers. If it can exist as the two isomers, draw both as a condensed structure.

(a) H₂C=CHCH₂CH₃

For each of the following compounds, indicate whether or not it can exist as cis–trans stereoisomers. If it can exist as the two isomers, draw both as a condensed structure.

(d)

For each of the following compounds, indicate whether or not it can exist as cis–trans stereoisomers. If it can exist as the two isomers, draw both as a condensed structure.

(c)

The structure of vitamin A is shown in Problem 4.54. Is the double bond nearest the ring on the carbon chain cis or trans?

The vision process in animals involves the change of one double bond in retinal from its cis form to its trans form. The structures of cis and trans retinal are shown below. Label which is cis and which is trans.

Determine whether each of the following is the cis or the trans stereoisomer: 

(c)

Determine whether each of the following is the cis or the trans stereoisomer:

(b)

Draw the skeletal structure and give the name and omega number of the following fatty acid:

CH₃CH₂CH₂CH₂CH₂HC=CHCH₂HC=CHCH₂CH₂CH₂CH₂CH₂CH₂CH₂COOH

Mark the chiral centers in the following molecules, if any, with an asterisk (*).

(a)

Mark the chiral centers in the following molecules, if any, with an asterisk (*).

(d)

Mark the chiral centers in the following molecules, if any, with an asterisk (*).

(d)

Are the following compounds structural isomers, cis–trans isomers, or enantiomers?

(c) 

Draw the enantiomer of each of the following compounds. If the compound is not chiral, state that fact.

(c)

Certain omega-3 fatty acids can be found only in animal sources, such as fatty fish. Two of these are eicosapentaenoic acid (EPA) [20:5] and docosahexaenoic acid (DHA) [22:6], both of which are ω-3 fatty acids. DHA has been shown to be important in healthy brain development, so it has recently been added to infant formulas. Breast milk is rich in DHA as long as the mother maintains a healthy diet that includes fish. Draw skeletal structures of the fatty acids EPA and DHA.

For each pair of molecules, identify the pair as:

A. structural isomers.

B. the same molecule (conformational isomers).

C. cis–trans stereoisomers.

D. different molecules.                                                                                                                                                                 

(b)