The Woodward–Hoffmann rules, devised by Robert Burns Woodward and Roald Hoffmann, are a set of rules in organic chemistry predicting the barrier heights of pericyclic reactions based upon conservation of orbital symmetry. The Woodward–Hoffmann rules can be applied to understand electrocyclic reactions, cycloadditions (including cheletropic reactions), sigmatropic reactions, and group transfer reactions. Reactions are classified as allowed if the electronic barrier is low, and forbidden if the barrier is high. Forbidden reactions can still take place but require significantly more energy. The Woodward...

An erratum or corrigendum (plurals: errata, corrigenda) (comes from Latin: errata corrige) is a correction of a published text. An erratum is most commonly issued shortly after its original text is published. Patches to security issues in a computer program are also sometimes called errata. As a general rule, publishers issue an erratum for a production error (i.e., an error introduced during the publishing process) and a corrigendum for an author's error. == Errata sheets == The Chicago Manual of Style describes an errata sheet as follows: "Errata, lists of errors and their corrections, may take...