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Related Concept Videos

Organic Compounds03:02

Organic Compounds

All living things are formed mostly of carbon compounds called organic compounds. The category of organic compounds includes both natural and synthetic compounds that contain carbon. Although a single, precise definition has yet to be identified by the chemistry community, most agree that a defining trait of organic molecules is the presence of carbon as the principal element, bonded to hydrogen and other carbon atoms. However, some carbon-containing compounds such as carbonates, cyanides, and...
Structure and Nomenclature of Ethers02:28

Structure and Nomenclature of Ethers

Structure and Bonding
Ethers are organic compounds with an ether functional group which is characterized by an oxygen atom connected to two — identical or different — alkyl, aryl, or vinyl groups. The C–O–C linkage in dimethyl ether — the simplest ether — has an approximately tetrahedral bond angle of 110.3 degrees. The oxygen atom is sp3- hybridized, with the C–O distance being about 140 pm.
Classification of Ethers
Based on their attached substituent groups, ethers can be classified into two...
Nomenclature of Alkynes02:39

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:
Aromatic Compounds: Overview01:25

Aromatic Compounds: Overview

In general, the term ‘aromatic’ indicates a pleasant smell or fragrance from fresh flowers, freshly prepared coffee, etc. In the early history of organic chemistry, many benzene derivatives were isolated from the pleasant odor oils of the plants. For example, vanillin was isolated from the oil of vanilla, methyl salicylate from the oil of wintergreen, and cinnamaldehyde from the oil of cinnamon. They all had a pleasant odor; hence the name aromatic was given.
In 1825, Faraday isolated benzene...
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-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.
Structures of Aldehydes and Ketones01:04

Structures of Aldehydes and Ketones

Vanillin—a flavoring agent in vanilla, cinnamaldehyde—a molecule responsible for the distinct smell of cinnamon, and acetone—a strong-smelling ingredient in nail polish removers, all belong to a class of carbonyl compounds called aldehydes and ketones (Figure 1). Although both aldehydes and ketones contain the characteristic carbonyl (C=O) bond, their chemical structures vary with respect to the groups directly attached to the carbonyl carbon.
In aldehydes (Figures 1a and 1b), the carbonyl...

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1,2-Didehydro[10]annulenes: structures, aromaticity, and cyclizations.

Armando Navarro-Vázquez1, Peter R Schreiner

  • 1Institute of Organic Chemistry, Justus-Liebig-University, Heinrich-Buff-Ring 58, 35392 Giessen, Germany.

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|June 2, 2005
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Summary

Computational studies reveal that C(10)H(8) 1,2-didehydro[10]annulenes favor a planar "heart" aromatic structure over a twisted form. This finding impacts understanding of their conversion to isonaphthalenes and dehydro Diels-Alder reactions.

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Area of Science:

  • Computational Chemistry
  • Organic Chemistry
  • Theoretical Chemistry

Background:

  • Understanding the conformational preferences and reactivity of annulene systems is crucial in organic chemistry.
  • Previous studies on related systems like C(10)H(10) [10]annulene provide context for the current investigation.
  • Dehydro Diels-Alder reactions involving phenylacetylenes are known to produce complex isomeric mixtures.

Purpose of the Study:

  • To computationally investigate the conformational landscape of C(10)H(8) 1,2-didehydro[10]annulenes.
  • To elucidate the unimolecular conversion pathway of these annulenes to isonaphthalenes (cyclic allenes).
  • To determine the mechanism underlying isomerizations observed in dehydro Diels-Alder reactions of phenylacetylenes.

Main Methods:

  • Density Functional Theory (DFT) using the B3LYP functional.
  • Single-reference coupled cluster with singles, doubles, and perturbative triples [CCSD(T)] calculations.
  • Multireference averaged quadratic coupled-cluster with singles and doubles and Davidson correction (MCQDPT2) post-Hartree-Fock methods.

Main Results:

  • The introduction of a linear alkynyl moiety in C(10)H(8) 1,2-didehydro[10]annulenes stabilizes a planar 'heart' aromatic conformer by over 6 kcal/mol (at the CCSD(T) level) compared to a localized C(2) 'twist' structure.
  • This conformational preference differs significantly from the closely related C(10)H(10) [10]annulene system.
  • Computational analysis indicates that isonaphthalenes undergo electrocyclic ring-opening to the 'heart' C(10)H(8) annulene via a low-energy barrier (approx. 15 kcal/mol).

Conclusions:

  • The planar 'heart' aromatic conformer is the preferred structure for C(10)H(8) 1,2-didehydro[10]annulenes due to reduced angle strain from the alkynyl group.
  • The low-barrier electrocyclic ring-opening of isonaphthalenes provides a viable mechanism for the observed isomerizations in dehydro Diels-Alder reactions of phenylacetylenes.
  • These computational findings offer valuable insights into the structure, stability, and reaction mechanisms of dehydroannulenes and related cyclic allenes.