Ornithine is decarboxylated to form putrescine and carbon dioxide. Draw the reaction and using bond energies, predict the enthalpy change for this reaction.
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.
Determine the structures of the molecules described in the following problems. Also note, in the combustion of N containing compounds, N2(g) is made.
4. Ornithine is decarboxylated to form putrescine and carbon dioxide. Draw the reaction and using bond energies, predict the enthalpy change for this reaction.
5. Ornithine decarboxylase (the enzyme that catalyzes the reaction in problem 1) is a target for ubiquitylation. In this process, ubiquitin (a small protein) is covalent linked to the target via an “isopeptide bond” between the side chain of lysine and the c-terminus carboxyl group of glycine. Water is released in this process. Predict the enthalpy change of this reaction using bond enthalpies.
6. Often we Hess’s law to determine enthalpies of reactions we are interested in using data from reactions we know. The heat of combustion of glycyl-glycine (dipeptide) is 1972 kJ/mol. The heat of combustion of glycine is -969kJ/mol. Is this enough information to determine the enthalpy of the reaction for forming the dipeptide (and associated products) from the amino acid? If it is, what is it?
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