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الكيمياء الصناعية | Calculating The Degree of Unsaturation (DoU) |
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 04:26 مساءً
date: 31-12-2019 |
Author : LibreTexts Project 
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If the molecular formula is given, plug in the numbers into this formula:
As stated before, a saturated molecule contains only single bonds and no rings. Another way of interpreting this is that a saturated molecule has the maximum number of hydrogen atoms possible to be an acyclic alkane. Thus, the number of hydrogens can be represented by 2C+2, which is the general molecular representation of an alkane. As an example, for the molecular formula C3H4 the number of actual hydrogens needed for the compound to be saturated is 8 [2C+2=(2x3)+2=8]. The compound needs 4 more hydrogens in order to be fully saturated (expected number of hydrogens-observed number of hydrogens=8-4=4). Degrees of unsaturation is equal to 2, or half the number of hydrogens the molecule needs to be classified as saturated. Hence, the DoB formula divides by 2. The formula subtracts the number of X's because a halogen (X) replaces a hydrogen in a compound. For instance, in chloroethane, C2H5Cl, there is one less hydrogen compared to ethane, C2H6.
For a compound to be saturated, there is one more hydrogen in a molecule when nitrogen is present. Therefore, we add the number of nitrogens (N). This can be seen with C3H9N compared to C3H8. Oxygen and sulfur are not included in the formula because saturation is unaffected by these elements. As seen in alcohols, the same number of hydrogens in ethanol, C2H5OH, matches the number of hydrogens in ethane, C2H6.
The following chart illustrates the possible combinations of the number of double bond(s), triple bond(s), and/or ring(s) for a given degree of unsaturation. Each row corresponds to a different combination.
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DoU
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Possible combinations of rings/ bonds
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||
|---|---|---|---|
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|
# of rings
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# of double bonds
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# of triple bonds
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1
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1
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0
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0
|
|
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0
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1
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0
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2
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2
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0
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0
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0
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2
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0
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0
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0
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1
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|
|
1
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1
|
0
|
Remember, the degrees of unsaturation only gives the sum of double bonds, triple bonds and/or rings. For instance, a degree of unsaturation of 3 can contain 3 rings, 2 rings+1 double bond, 1 ring+2 double bonds, 1 ring+1 triple bond, 1 double bond+1 triple bond, or 3 double bonds.
Example : Benzene
What is the Degree of Unsaturation for Benzene?
SOLUTION
The molecular formula for benzene is C6H6. Thus,
DoU= 4, where C=6, N=0,X=0, and H=6. 1 DoB can equal 1 ring or 1 double bond. This corresponds to benzene containing 1 ring and 3 double bonds.
However, when given the molecular formula C6H6, benzene is only one of many possible structures (isomers). The following structures all have DoB of 4 and have the same molecular formula as benzene.
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"إنقاص الوزن".. مشروب تقليدي قد يتفوق على حقن "أوزيمبيك"
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الصين تحقق اختراقا بطائرة مسيرة مزودة بالذكاء الاصطناعي
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قسم شؤون المعارف ووفد من جامعة البصرة يبحثان سبل تعزيز التعاون المشترك
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