degree of unsaturation

[aliss4]

Can somebody tell me why C5H5N has 4 degree of unsaturation?

thanks

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[LuckMC11]

Can somebody tell me why C5H5N has 4 degree of unsaturation?

thanks

4 degrees of unsaturation means it can have any combination of double bonds or rings, but has to add up to 4. in this molecule, it has 3 double bonds and 1 ring, so 3 + 1 = 4 degrees of unsaturation

 

[Pennpaki]

or u could simply use the formula:

.5( 2C +2 - H - X +N)

X is halogens here

 

[Troyvdg]

Can somebody tell me why C5H5N has 4 degree of unsaturation?

thanks

formula is 1 + the # of carbons = 6
subtracted half the number of hydrogens
and + .5 for nitrogen

6-2.5= 3.5 + .5 = 4

 

[highhopee]

To find Degree of Unsaturation of C5H5N (1):
base formula = C5H12
base formula with N = C5H13N (2)

Subtract Total H of (1) from Total H of (2): 13 - 5 = 8 (3)

Divide (3) by 2: 8/2 = 4

Therefore, C5H5N has a Degree of Unsaturation of 4.

 

[aquafoam]

I use this formula (I know it differs from textbook to textbook):

[(2C+2)+N-H]/2

Note that H's can also include halogens.

 

[LuckMC11]

why do you add N but subtract halogens?

 

[herkulease]

why do you add N but subtract halogens?

you count halogens as a hydrogen because halogen's can only form 1 bond like hydrogens.

 

[LuckMC11]

oh ok and everything else you add?

 

[Ibraiz]

Highhopee, how are you getting the formula "base formula with N = C5H13N (2)"?

I know you can C5H12 from Cn Hn+2 and based on this I am using this formula and subtracting it from C5H5N means 12 from the alkane formula subtract it from 5H and 1N

12 - 6 = 6 / 2 = 3 degree of unsaturation. I know the answer is wrong and I understand using C2H13N would give me the correct answer but where is this formula coming from because

alkane = Cn Hn+2
alkene = Cn Hn
alkyne = Cn Hn-2

 

[highhopee]

Highhopee, how are you getting the formula "base formula with N = C5H13N (2)"?

I know you can C5H12 from Cn Hn+2 and based on this I am using this formula and subtracting it from C5H5N means 12 from the alkane formula subtract it from 5H and 1N

12 - 6 = 6 / 2 = 3 degree of unsaturation. I know the answer is wrong and I understand using C2H13N would give me the correct answer but where is this formula coming from because

alkane = Cn Hn+2
alkene = Cn Hn
alkyne = Cn Hn-2

Hey Ibraiz
I'll show you step by step,
To find Unsaturation for C5H5N,
First find the base formula, meaning find the molecular formula
that is an alkane with C = 5 and associated amount of Hydrogens.
This is easy to find because you know that the ends will have 3 hydrogens and the middle methylenes have 2 hydrogens.
So it is (2x3H) + (3x2H) = 12H
Thus, we have C5H12

Now, find the base formula with 1 Nitrogen.
For group V (N, P, As, Sb, Bi), add 1H to your base formula because
if we have CH and attach N, we get CNH2
We went from 1H to 2H, meaning we add 1 H.

For group VI (O, S, Se, Te),
we don't add nor subtract Hydrogens because
if we have CH and add O, we get COH
There is no change in # of hydrogens.

For group VII (F, Cl, Br, I),
we subtract 1H because
if we add these atoms, we go from CH to CF
There is a change in number of hydrogens from 1H to 0.

So our base formula was C5H12.
Add 1N. Thus we now have C5H13N
Subtract the # of hydrogens that we get with N (C5H13N)
to the # of hydrogens that was asked (C5H5N)

13 - 5 = 8

Now, divide 8 by 2.

Voila, our degree of unsaturation is 4! =)

 

[Ibraiz]

Thanks for the explanation, so for C5H502 the base formula would be C5H502 and we subtract this from C5H12 (since we don't add nor subtract an H because its from the Group VI)

12-5 = 7 / 2 = 3.5 degree of unsaturation?

 

[UCB05]

Yes, except you wouldn't get that formula. It would have an even number of hydrogens to be a feasible molecule, and would have a whole-number degree of unsaturation.