Bluffton University

Organic Chemistry

Using Molecular Models

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Double-bond pieces include several types: end-pieces, which are gray; gray double bonds; and half-bonds which are either gray or red. The gray pieces are used to represent carbon atoms and carbon-carbon double bonds; in order to represent a carbon-carbon double bond, snap a gray end-piece into each end of one of the gray double bonds.

Build a model of ethene ("ethylene"), and compare it to the models shown below. The "bonds" are arranged at normal trigonal planar angles of 120°. Notice that the online model does not show the double bond!
ethene ethene

Carbon-oxygen double bonds - carbonyl groups - may be represented using the gray and red half-bonds. To represent a carbonyl group, first snap together one red and one gray half-bond; then snap a gray end-piece into the gray end of the double bond.

methanal methanal

Carbon-nitrogen double bonds are rarer in organic chemistry, and the fact that the nitrogen's valence is not filled means that a group may be bonded to nitrogen. To represent a carbon-nitrogen double bond, take a gray double-bond piece. Snap a gray end-piece into one end to represent carbon, and a blue tetrahedral piece into the other end for nitrogen.

methanal imine methanimine

Triple bonds are represented using the gray triple-bond pieces. Each piece represents two carbon atoms with a triple bond between them and one open valence for each atom. Notice that triple bonds have a normal bond angle of 180°. Carbon-nitrogen triple bonds are also possible (such bonds are referred to as cyano or nitrile groups), but there is no distinct way to represent them with a "sticks-only" kit. However, Darling Models has recently added Atom Visions pieces to its kits which allow one to represent ball-and-stick models; using these pieces, one can distinguish unambiguously between e.g. propyne and acetonitrile.

methanal ethyne
methanal propyne: stick model propyne: ball-and-stick model
methanal acetonitrile: stick model acetonitrile: ball-and-stick model

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Copyright © 1998, 1999, 2000, 2003, 2007 by Daniel J. Berger. This work may be copied without limit if its use is to be for non-profit educational purposes. Such copies may be by any method, present or future. The author requests only that this statement accompany all such copies. All rights to publication for profit are retained by the author.