# Step 7: Sometimes compounds without rings have the same molecular formula and the same connectivity (what is attached to what) is the same, but there are still distinct isomers. When this happens, the compounds have possible conformations that might be mirror images of each other. Two compounds that are mirror images of each other but are nonetheless different are called enantiomers or optical enantiomers (as they interact with polarized light differently). Your two hands have this property. For each of the following pairs, make models of both structures at the same time, and then indicate with a check mark if they are the same or are different, are mirror images of each other. To do this see if you can somehow manipulate one so that it looks exactly like the other. same Step 8: Based on these three examples, write a simple rule to tell which compounds have a Pair G: different mirror image that is different, which compounds have an enantiomer. same Pair H: different

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ANSWER step 7:

For each compound, draw the 3D model (see table below). Then, for each pair, rotate one molecule of the pair and verify if after rotation it looks like the other molecule (see table below).

• Both molecules of pair G could be rotate to the position showed in table. Then both molecules are the same compound
• Both molecules of pair H could be rotate to the position showed in table. Then both molecules are the same compound
• For pair I, it does not matter how you rotate the molecule A, it is always different from molecule B. Then both molecules are the different compounds and are enantiomers.

ANSWER step 8:

• Example 1: the C atomo have only two differents groups (1 Cl and 3 CH3) => pair G = same compound
• Example 2: the C atomo have only three differents groups (1 Cl, 1 H and 2 CH3) => pair H = same compound
• Example 3: the C atomo have four differents groups (1 Cl, 1 H, 1 CH3 and 1 CH2CH3) => pair I = different compounds (enntiomers)

​​​​​​​Rule: If a compound have a C atom with four differents groups, then, the mirror image of this compound will be a different compound (an enantiomer)