There is a revised video of this part of the course with chapter divisions on a time scale in improved quality under the following link: • NEW - Organic Chemistry Part 15: Halo... HALOGENALKANE: Structure [00:08:20] / Nomenclature [00:14:30] / Properties [00:18:40] / Reactivity [00:28:20] / Synthesis [00:37:40] / Leaving groups [00:39:10] / Bimolecular nucleophilic substitutions SN2 [00:48:10] / Walden inversion [00:58:10] / Influence of substrate backbone [01:07:20] / Nucleophilicity [01:13:20] In part 15 you will learn about the class of substances known as haloalkanes. These are hydrocarbons with singly bonded halogen atoms. First, we will look into the question of why benzene is carcinogenic (00:01:30). This is followed by an overview of the functional groups with a carbon-heteroatom bond CX (00:05:30). Carbon-halogen bonds can be found, for example, in the thyroid hormone thyroxine, in the sweetener sucralose and in the insecticide DDT (00:08:20). Low-molecular halogenated hydrocarbons are used as coolants and organic solvents (00:12:10). Since halogens are more electronegative than carbon, the carbon-halogen bond is polarized to the halogen atom (00:18:40). This creates a negative partial charge on the halogen atom and a positive one on the C atom. Nucleophiles therefore prefer to attack the C atom of the CX bond (00:28:20), while electrophiles and Lewis acids prefer to bind to the halogen atom. Haloalkanes preferentially undergo nucleophilic substitutions or eliminations to form alkenes (00:35:30). In both types of reactions, the halogen atom acts as a leaving group. Since chloride, bromide and iodide anions are very weak Broensted bases, these monatomic ions are good leaving groups (00:39:10). Organohalogen compounds are synthesized by radical halogenation of alkanes, electrophilic additions of halogens or HX to alkenes and electrophilic aromatic substitutions (00:37:40). In the second half of the course, so-called bimolecular nucleophiles learn about substitutions (SN2) (00:48:10). These transformations take place in a single reaction step in which the bond to the leaving group is broken heterolytically and the bond to the nucleophile is formed at the same time. In the transition state, the C atom at which the exchange takes place has five bonds and is coordinated in a trigonal-bipyramidal manner (00:52:40). These substitutions with a reaction order of two proceed under stereochemical Walden inversion (00:58:10). Due to the high number of substituents in the transition state (01:07:20), methyl and primary halides are particularly well suited for SN2 reactions. SN2 substitutions do not occur on sp2-hybridized C atoms (01:11:50). In addition to the carbon backbone, the strength of the nucleophile also has a significant influence on the reaction rate (01:13:20). The quality of a nucleophile is determined by Broensted basicity and the electronegativity and steric shielding of the nucleophilic atom (01:16:00). The playlist with all parts of the course and live streams can be found at: • Organic Chemistry A description of the contents of all course parts and the script are available at the following link: https://www.peterhuylab.de/youtube/ The password for the “teaching materials” area with the course script can be obtained from Prof. Huy (peter.huy[at]uni-rostock.de). For this course unit, chapters 1 - 17 of “Chapter 8: Halogenalkanes and Alcohols” were used. This video is an unedited recording of the live streaming of the lecture “Organic Chemistry for Life Sciences and Biology Teaching” by Prof. Dr. Peter Huy from June 2nd, 2021 at the Institute of Chemistry at the University of Rostock.