Final answer:
The most logical transition word for the given sentence about a flipped chiral molecule is 'By contrast,' as it highlights the contrasting nature between achiral and chiral molecules that are non-superimposable mirror images.
Step-by-step explanation:
The most logical transition to complete the sentence about a flipped chiral molecule would be C. By contrast. This phrase introduces the difference between an achiral molecule, which is symmetrical and identical to its mirror image, and a chiral molecule. Chiral molecules have handedness, similar to the way our hands are mirror images that are not superimposable, just as a right-hand glove does not fit on the left hand. In chemistry, chiral molecules, like enantiomers, have the same chemical structure but differ in their three-dimensional arrangement of atoms, making them non-superimposable mirror images, which is a key aspect of stereochemistry.
Enantiomers are notable examples of chiral molecules. L-alanine and D-alanine are examples of enantiomers, where one is the mirror image of the other and thus have different optical activities, a property that allows them to rotate polarized light in different directions. When considering molecules with chiral centers, such as those found in amino acids or sugars like glucose, this chirality plays a critical role in biological systems and reactions, including the interactions with chiral reagents like enzymes.