Saturated or Unsaturated Chemistry???

Question

Im stuck on this one! :( can anyone help????

Giving reasons for your answers, indicate whether each of the following formulas is saturated, unsaturated, or impossible to exist.
A. C2H5 B. C4H10 C. C3H12 D. C2H2 E. CH2

Answer 1

Saturated means there are only single bonds between the carbons.

A. Does not exist (does not obey the octet rule)
B. Saturated (it is an alkane and only has single bonds)
C. Does not exist (does not obey the octet rule)
D. Unsaturated. (Its an alkyne and has a triple bond)
E. Does not exist (does not obey the octet rule)

Answer 2

Saturated hydrocarbons obey the formula CnH2n+2. So the number of H atoms in a formula subtracted from the saturated hydrocarbon (of the same no of carbon atoms) divided by 2 gives a clue to structure.

A C2H5 can't exist. Degree of saturation 0.5

B C4H10. Degree of saturation 0. This is a saturated alkane - propane.

C C3H12 Most H atoms can have is 8. Does not exist

D C2H2 Degree of saturation is 2. Can be two double bonds (not possible here - only 2 C atoms) or one triple bond. This is an unsaturated hydrocarbon - acetylene.

E CH2 Does not exist. This group is known as methylene eg C2H2Cl2 is methylene chloride or dichloromethane.

Answer 3

Your question involves the so-called points of saturation. The formula for a hydrocarbon is CnH2n+2, if the hydrocarbon is saturated. For every ring in the structure (triangle, square, pentagon, hexagon) there are 2 taken away from the saturated formula. Likewise for every double bond, >C=C<, >C=O.

A. C2H5 cannot exist by itself. It is an ethyl group. Put another H on it, and it is ethane, C2H6. This formula follows the pattern CnH2n+2, and ethane is saturated.
B. C4H10 is CnH2n+2, so it is saturated.
C. C3H12 is CnH2n+6, which is impossible.
D. C2H2 is of the type CnH2n-2. So it has two points of unsaturation. Because two carbons cannot form a ring, this compound is HC*triple bond*CH
E. CH2 is something your teacher may say does not exist. Yet, in organic chemistry, this species can exist briefly as methylene carbene or diradical.

Answer 4

Carbon has a valence of 4, hydrogen a valence of 1. A fully saturated hydrocarbon has CnH(2n+2) relationship. Simple alkenes are CnH2n and alkynes are CnH(2n-2).
Simple hydrocarbon unsaturation level can be easily calculated where only carbon and hydrogen occur in the formula (for formulae having 2 or more carbon atoms) using the mathematical formula:

# sites of unsaturation U = (2n-m+2)/2,
where n= # of carbon atoms and
m= total # of hydrogen atoms in the formula

The result must be a real number, 0, 1, 2, 3 etc. If you get a fraction, the hydrocarbon is not a neutral species, but rather exists as a carbon radical.

C2H5, n=2 and m=5
(2*2-5+2)/2 = 1/2 radical

C4H10, n=4 and m=5
(2*4-10+2)/2 = 0 saturated (no sites of unsaturation, such as butane)

C3H12, n=3 and m=12
(2*3-12+2)/2 = -2 does not exist

C2H2, n=2 and m=2
(2*2-2+2)/2 = 2...two sites of unsaturation
(ethyne H-C triple bond C-H)

The last one has only 1 carbon atom and requires 4 hydrogen atoms to exist (unless it is an unstable radical species).

Practice: C3H8 (propane), C5H10 (cyclopentane), C6H6 (benzene), C5H8, (pentyne or cyclopentene), C7H18 (?)

Answer 5

A. C2H5 Unsaturated C2H6 is saturated
B. C4H10 Saturated Maximun # of H's
C. C2H2 Unsaturated
D. CH2 Impossible to exsist C must make 4 bonds and each H can only make one

Mark

Answer 6

B. C4H10
H H H H
H-C-C-C- C-H
H H H H
All C bonds are filled with H+. Therefore the molecule is SATURATED.

A. C2H5
H-H
H-C-C-
H-H
NOT SATURATED. Room for ONE MORE H bonding.

c. C3H12

H-H-H
H2-C-C-C--H2
H-H-H
All C bonds H bonded, therefore SATURATED. But, don't really see how this can exist. It APPEARS as though ONLY !) could go in here!

D. C2H2

H-C=C-H

IF THIS MOLECULE HAS A TRIPLE BOND, it COULD be saturated. SINGLE BONDED, NO!

E. CH2
?
H-C-H
?

NO. NOT SATURATED!

Answer 7

saturated chains do not have double or triplebond between Carbon atoms where as unsaturated chains have atleast one or more double or triple bond. Unsaturated hydrocarbons undergo hydrogenation.

Answer 8

I dont know about the others but CH2 is not a real because the simplest hydrocarbon is CH4 or methane and the one C2H2 is called acetylene.