An Easily Constructed Helix Model Shukichi Yamana Department of Kyoushoku Education, Kinki University, Kowakae, Higashi Osaka 577, Japan
A simple type helix model i s useful for teachine stereochemistry (especially oflthe mnformation of alkane derivative having optical rotatory power). This mo: del can be made easily by using several sealed, empty envelopes of t h e same s h a p e a n d magnitude. The orinciole of the method i s first to produie several topless tetrahedra and next to combine them with each other to yield a h e l i x model. T h e s t e p s (illustrated i n the figure a n d picture) are given below. (1) The first set of three figures shows the starting canfigur-
ation, which is produced hy steps 1-26) of the previously published article.' But here, only two marks of two valleys (1 and 3) a r e exchanged for each other and all the other marks are used without anv correction. In oder w dkngulsh thls remarked unit from theongmally marked one, the former is labeled "Right-handed Helix unit" (abbreviated to RHunit). (2) Similarly, several (no less than six) more RH-units are produced from the other sealed, empty envelopes. However, all marks of the second and third RT-units are identified in the figure by their symbols 'and ", respectively. (3) The sharpest top A' (united with F)of the second RHunit is inserted into the hole of the first RH-unit so that three sides of the semnd RHunit, ( I*'A', FA', and 3*'A') touch three valleys (1,2, and 3) of the first RH-unit, respectively. Of course, this combination of two RH-units has a hole and is a starting nucleus for the further multinliention. ~ - - ~ - ~ - ~ . ( 4 ) Repeating-step 3 above, the remaining RH-units arejoined to the ~imrtingnucleus one after another, and they are
taped to produce a model of a right-handed helix. Similarly, a lefehanded helix model can be made by the following procedure. (5) A olane of the same shaw and maenitude as the startine plane given in ~ t r 1 p of this article, is turned over and all
marks am put in parentheses. 'Yamana, S. J. Chem. Educ. 1992,69,216.
(6) Oblique lines are drawn to shade the topless triangle (3*)(Q)(3XZ*XA).A shaded face will he effective to grasp relative orientations of all faces belonging to component units in a left-handed helix model (7) By steps similar to 28-30 of the previously published arti-
cle,' a distorted topless tetrahedron is produced from this reversed plane, and this is labeled "Left-handed Helix unit" (abbreviated to LH-unit).
(8)By steps similar to 2-4 above, several LH-units are produced from the other reversed planes, and they are eombined with each other. This cluster of LH-units is t a ~ e to d produce a left-handed helix model.
Volume 69 Number 4 April 1992
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