Analytical chemistry
Double bond equivalent
不飽和度
Structure????
Alkane
: CnH2n+2
Alkene (with one C=C) : CnH2n
Benzene
: C6H6
Aspirin
: C9H8O4
Benzamide
: C7H7NO
Structural
Formula????
Double bond equivalent 不飽和度 (DBE)
• Total number of rings and π bond (double bond, triple bond)
• After you determined the molecular formula
𝟏
𝑫𝑩𝑬 = (𝑪 × 𝟐 + 𝟐 − 𝑯 − 𝑿 + 𝑵)
𝟐
No. of Carbon
No. of Hydrogen
No. of Nitrogen
No. of Halogen
e.g. Alkane : CnH2n+2
𝟏
𝑫𝑩𝑬 =
𝑪×𝟐+𝟐−𝑯−𝑿+𝑵
𝟐
𝐷𝐵𝐸 =
1
2
𝑛 × 2 + 2 − 2𝑛 + 2 − 0 + 0
𝐷𝐵𝐸 = 0
→ Saturated (no ring/double bond/triple bond)
e.g. Alkene (with one C=C) : CnH2n
𝟏
𝑫𝑩𝑬 =
𝑪×𝟐+𝟐−𝑯−𝑿+𝑵
𝟐
1
𝐷𝐵𝐸 =
𝑛 × 2 + 2 − 2𝑛 − 0 + 0
2
𝐷𝐵𝐸 = 1
→ Consistent with ONE double bond
e.g. Benzene : C6H6
𝟏
𝑫𝑩𝑬 =
𝑪×𝟐+𝟐−𝑯−𝑿+𝑵
𝟐
1
𝐷𝐵𝐸 =
6×2+2−6−0+0
2
𝐷𝐵𝐸 = 4
→ Consistent with ONE ring + THREE C=C
e.g. Aspirin : C9H8O4
𝟏
𝑫𝑩𝑬 =
𝑪×𝟐+𝟐−𝑯−𝑿+𝑵
𝟐
1
𝐷𝐵𝐸 =
9×2+2−8−0+0
2
𝐷𝐵𝐸 = 6
→ Consistent with ONE benzene ring and TWO C=O
e.g. Benzamide : C7H7NO
𝟏
𝑫𝑩𝑬 =
𝑪×𝟐+𝟐−𝑯−𝑿+𝑵
𝟐
1
𝐷𝐵𝐸 =
7×2+2−7−0+1
2
𝐷𝐵𝐸 = 5
→ Consistent with ONE benzene ring and ONE C=O