Chapter 3-1. Structure of Cycloalkanes and Cycloalkenes
Recommended Article: 【Organic Chemistry】 Chapter 3. Alkanes
1. Structure of Cycloalkanes
2. Structure of Cycloalkenes
1. Structure of Cycloalkanes
⑴ Cyclopropane
① Newman projection: The dihedral angle of C-H on two adjacent carbons can be 0° or an ambiguous angle
② Halocyclopropane can perform syn -periplanar E2 reaction
Figure 1. Structure of cyclopropane
⑵ Cyclobutane
① Newman projection: The dihedral angle of C-H on two adjacent carbons can be 60°, 180°
② Halocyclobutane can perform anti -periplanar E2 reaction
③ Planar structure and butterfly structure
○ The planar structure has much greater torsional strain than the butterfly structure
○ The butterfly structure (88°) has greater bond angle strain than the planar structure (90°) due to smaller bond angles
○ The butterfly structure is more stable because the difference in torsional strain is much greater than the bond angle strain
Figure 2. Butterfly structure of cyclobutane
⑶ Cyclopentane
① Newman projection: The dihedral angle of C-H on two adjacent carbons in the square part can be 0° or an ambiguous angle
② Halocyclopentane with one halogen substituted in the square part can perform syn -periplanar E2 reaction
Figure 3. Structure of cyclopentane
⑷ Cyclohexane
① Stability comparison of conformers: Stability order is chair > twist boat > boat > half chair
○ Strictly speaking, the chair form and twist boat are conformers, while boat and half chair are transition states
② Chair form cyclohexane
○ The dihedral angle of C-H on two adjacent carbons can be 60°, 180°
○ Halocyclohexane can perform anti -periplanar E2 reaction
Figure 4. Chair form cyclohexane and ring flip
③ Twist boat form cyclohexane
Figure 5. Structure of twist boat form cyclohexane
④ Boat form cyclohexane
Figure 6. Structure of boat form cyclohexane
⑤ Half chair form cyclohexane
⑸ Cycloheptane
① Chair form cycloheptane
Figure 7. Structure of chair form cycloheptane
② Boat form cycloheptane
Figure 8. Structure of boat form cycloheptane
⑹ Cyclooctane
① Chair form cyclooctane
Figure 9. Chair form cyclooctane
② Tube form cyclooctane
Figure 10. Tube form cyclooctane
③ Boat-boat form cyclooctane
Figure 11. Boat-boat form cyclooctane
2. Structure of Cycloalkenes
⑴ Overview
① Cyclopentene [3] ~ cycloheptene [7]: Only cis structure exists
② Cyclooctene [8] ~ cycloundecene [11]: cis structure is more stable than trans structure
③ Cyclododecene [12]: Stability of cis and trans structures is similar
④ Cyclotridecene [13]: trans structure is more stable than cis structure
⑵ Cyclohexane
① Cyclohexene
Figure 12. Structure of cyclohexene
② Cyclohex-1,3-diene
Figure 13. Structure of cyclohex-1,3-diene
③ Cyclohex-1,4-diene
Figure 14. Structure of cyclohex-1,4-diene
⑶ Cycloheptatriene
① If the carbon without a double bond becomes a carbocation, it satisfies aromaticity; that is, it becomes a planar heptagon
Figure 15. Cycloheptatriene
⑷ Cyclooctatetraene
① Does not satisfy planarity, hence does not satisfy aromaticity
Figure 16. Cyclooctatetraene
⑸ [10]-Annulene
① Although it has 4n+2 π-electrons, it does not satisfy aromaticity due to lack of planarity
② Three types exist; all cis, one trans, or two trans
Figure 17. Structure of [10]-annulene
Input: 2019.03.15 14:14