Using bond energies from the table, estimate ΔH for the reaction below. The OH group on the product side is attached to a carbon. CH2=CH2(g) + H2O(g) ↔ CH3CH2OH(g)
Reactive Intermediates
In chemistry, reactive intermediates are termed as short-lived, highly reactive atoms with high energy. They rapidly transform into stable particles during a chemical reaction. In specific cases, by means of matrix isolation and at low-temperature reactive intermediates can be isolated.
Hydride Shift
A hydride shift is a rearrangement of a hydrogen atom in a carbocation that occurs to make the molecule more stable. In organic chemistry, rearrangement of the carbocation is very easily seen. This rearrangement can be because of the movement of a carbocation to attain stability in the compound. Such structural reorganization movement is called a shift within molecules. After the shifting of carbocation over the different carbon then they form structural isomers of the previous existing molecule.
Vinylic Carbocation
A carbocation where the positive charge is on the alkene carbon is known as the vinyl carbocation or vinyl cation. The empirical formula for vinyl cation is C2H3+. In the vinyl carbocation, the positive charge is on the carbon atom with the double bond therefore it is sp hybridized. It is known to be a part of various reactions, for example, electrophilic addition of alkynes and solvolysis as well. It plays the role of a reactive intermediate in these reactions.
Cycloheptatrienyl Cation
It is an aromatic carbocation having a general formula, [C7 H7]+. It is also known as the aromatic tropylium ion. Its name is derived from the molecule tropine, which is a seven membered carbon atom ring. Cycloheptatriene or tropylidene was first synthesized from tropine.
Stability of Vinyl Carbocation
Carbocations are positively charged carbon atoms. It is also known as a carbonium ion.
Using bond energies from the table, estimate ΔH for the reaction below. The OH group on the product side is attached to a carbon.
CH2=CH2(g) + H2O(g) ↔ CH3CH2OH(g)
|
Bond Energies, kJ/mol |
|||||||||
|
Single Bonds |
|||||||||
|
|
H |
C |
N |
O |
S |
F |
Cl |
Br |
I |
|
H |
432 |
|
|
|
|
|
|
|
|
|
C |
411 |
346 |
|
|
|
|
|
|
|
|
N |
386 |
305 |
167 |
|
|
|
|
|
|
|
O |
459 |
358 |
201 |
142 |
|
|
|
|
|
|
S |
363 |
272 |
--- |
--- |
286 |
|
|
|
|
|
F |
565 |
485 |
283 |
190 |
284 |
155 |
|
|
|
|
Cl |
428 |
327 |
313 |
218 |
255 |
249 |
240 |
|
|
|
Br |
362 |
285 |
243 |
201 |
217 |
249 |
216 |
190 |
|
|
I |
295 |
213 |
--- |
201 |
--- |
278 |
208 |
175 |
149 |
|
Multiple Bonds |
|||||
|
C=C |
602 |
C=N |
615 |
C=O |
799 |
|
CºC |
835 |
CºN |
887 |
CºO |
1072 |
|
N=N |
418 |
N=O |
607 |
S=O (in SO2) |
532 |
|
NºN |
942 |
O2 |
494 |
S=O (in SO3) |
469 |
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