Advices For Studying Organic Chemistry

R

R

R

R

R

H

R

R

H

H

R

R R

R H

H

R

H

R

H

H

H

R

H

H

H

H

H

Tetrasubstituted Trisubstituted Monosubstituted Unsubstituted

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Disubstituted

7.4 CYCLOALKENES

1. The rings of cycloalkenes containing five carbon atoms or fewer exist only in the
   cis form.

H C

2 C C

H

H

H 2 C

H 2 CC

C

H

H

H 2

C

H 2 C

CH

2

H

H

H 2

H C

2 C

H 2 C C

H 2

H

H

Cyclopropene Cyclobutene Cyclopentene Cyclohexene
Figure 7.3 cis-Cycloalkanes.

2. There is evidence that trans-cyclohexene can be formed as a very reactive
   short-lived intermediate in some chemical reactions.

H 2 C

H 2 C

CH 2

CH 2

C

C

H

H

Figure 7.4 Hypothetical trans-cyclohexene. This molecule is apparently too
highly strained to exist at room temperature.

3. trans-Cycloheptene has been observed spectroscopically, but it is a substance with
   very short lifetime and has not been isolated.


4. trans-Cyclooctene has been isolated.
   
   
   1. The ring of trans-cyclooctene is large enough to accommodate the geometry
      required by trans double bond and still be stable at room temperature.