On the structure of "5-nitrosotropolone"
Ai Ito1, Hideaki Muratake, Koichi Shudo
1Research Foundation Itsuu Laboratory, 2-28-10 Tamagawa, Setagaya-ku, Tokyo 158-0094, Japan.
The Journal of Organic Chemistry
|December 31, 2008
Summary
5-nitrosotropolone exists predominantly as the oxime tautomer (1B), not the nitroso form (1A). Spectroscopic analysis confirmed this structure, with UV shifts indicating a dissociated form in dilute solutions.
Area of Science:
- Organic Chemistry
- Spectroscopy
- Chemical Structure Elucidation
Background:
- The tautomerism of 5-nitrosotropolone has been a long-standing debate in chemical literature.
- Distinguishing between the nitroso (1A) and oxime (1B) forms is crucial for understanding its chemical properties.
Purpose of the Study:
- To definitively determine the preferred tautomeric structure of 5-nitrosotropolone.
- To investigate the influence of solution conditions on the compound's spectral properties.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy was employed to analyze the molecular structure.
- Ultraviolet (UV) spectroscopy was used to study electronic transitions and solution behavior.
Main Results:
- Spectroscopic data analysis strongly supports the oxime structure (1B) as the predominant form of 5-nitrosotropolone.
- A bathochromic shift in UV absorption at dilute concentrations suggests the presence of a dissociated species (3).
Conclusions:
- The tropoquinone-5-monoxime tautomer (1B) is favored over the nitroso form (1A).
- Solution dynamics, particularly dissociation at low concentrations, influence the observed UV spectra.
More Related Videos
Related Concept Videos
01:19Nitrosation of Enols
The nitrosation reaction is one of the methods of preparing 1,2-diketones. The enol tautomer of the starting ketone reacts with sodium nitrite in hydrochloric acid, generating the 1,2-diketone after hydrolysis.
01:28Structures of Carboxylic Acid Derivatives
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
01:202° Amines to N-Nitrosamines: Reaction with NaNO2
Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.
01:13Five-Membered Heterocyclic Aromatic Compounds: Overview
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom, respectively.
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
01:12Preparation of Nitriles
One of the common methods to prepare nitriles is the dehydration of amides. This method requires strong dehydrating agents like phosphorous pentoxide or boiling acetic anhydride for converting amides to nitriles. Another reagent namely, thionyl chloride also accomplishes the dehydration of amides, where amide acts as a nucleophile. The first step of the mechanism involves the nucleophilic attack by the amide on the thionyl chloride to form an intermediate. In the next step, the electron pairs...