Download
Lignans and neolignans are a large group of natural products characterized by the coupling of two C6C3 units. For nomenclature purposes the C6C3 unit is treated as propylbenzene and numbered from 1 to 6 in the ring, starting from the propyl group, and with the propyl group numbered from 7 to 9, starting from the benzene ring. With the second C6C3 unit the numbers are primed. When the two C6C3 units are linked by a bond between positions 8 and 8′ the compound is referred to and named as a lignan. In the absence of the C-8 to C-8′ bond, and where the two C6C3 units are linked by a carbon–carbon bond it is referred to and named as a neolignan. The linkage with neolignans may include C-8 or C-8′.
Where there are no direct carbon–carbon bonds between the C6C3 units and they are linked by an ether oxygen atom the compound is named as an oxyneolignan. The nomenclature provides for the naming of additional rings and other modifications following standard organic nomenclature procedures for naming natural products. Provision is included to name the higher homologues. The sesquineolignans have three C6C3 units, and dineolignans have four C6C3 units.
Pure & Appl. Chem., Vol. 72, No. 8, p. 1493–1523, 2000
IUPAC Recommendations
© 2000 IUPAC
IUPAC permission is acknowledged
Download
Contents
1. Introduction
2. Definitions
3. Nomenclature
3.1. Introduction
3.2. Coordination nomenclature
3.2.1. Selection of the central atom
3.2.2. Radicals with net charges
3.2.3. Attached atoms or groups of atoms
3.2.4. The radical dot
3.2.5. Examples
3.3. Substitutive nomenclature
Pure Appl. Chem., Vol. 72, No. 3, pp. 437–446, 2000.
IUPAC Recommendations 2000
© 2000 IUPAC
IUPAC permission is acknowledged
Abstract
The mathematical complexity involved in the quantum theory is beyond the level of general chemistry courses and has led to the use of excessive simplifications. Although this situation is being discussed in the literature over the past 20 years, an inconsistent approach to the principles of quantum theory and experimental observations, even though emphasizing the importance of the Schrödinger equation are still frequently found, not only in general chemistry texts but also in physical – chemical texts. Fundamental concepts such as wave function, orbitals, levels of energy and orbital energy are used incorrectly or in an imprecise way. The incorrect application of ideas creates difficulties later, such as those observed in the interpretation of atomic and molecular spectra. This article aims to contribute to the teaching of fundamental concepts necessary to build a qualitative model for atoms with several electrons (or polyeletronic). This is performed by discussing the foundations and limitations of the orbital model and analyzing the main erroneous concepts found, highlighting their origin.
Keywords
Hartree-Fock model, orbital model, orbital energy, Aufbau principle, quantum numbers, electronic configuration
Author
Noemí Marta Torres
Cátedra de Química, Ciclo Básico Común, Universidad de Buenos Aires
Translated by
João C. de Andrade
Revised by
Carol H. Collins
