Question

how can we count isomers

Answer 1

YOUR ANSWER....^_^..

=》In order to figure out the more advanced problem we first considered rooted trees with each vertex having degree at most 3. For further simplification we considered planar trees, i.e. symmetric trees were counted as distinct. Let an denote the number of such trees with exactly n vertices. We define the generating polynomial (power series).
=》The point you should get from this example is that three sequentially attached sp3 carbon atoms can be drawn in a variety of ways, but are still the same structure. With additional carbon atoms (4, 5, 6…) the possibilities increase, but the feature to focus on when deciding if two structures are identical or different is the length of the carbon chain and the length and positions of its branches. Whether you have 3,4,5, or more carbon atoms zig-zagged in any manner possible, you can always redraw it in a simpler straight chain form. The straight chain representation is easier for you to work with, so choose it as your method of drawing a 2D structure (even if it is changing its shape thousands of times per second). Drawing your structures with a straight chain, as much as possible, will give you the best chance of not overlooking a structure. We will use this approach in our subsequent.
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