When we try to superimpose A onto B, we find that we cannot do it. Electronic configuration of carbon is 2, 4. Complete answer: Carbon forms covalent bonds with other atoms or groups of atoms. Tetravalency of carbon means presence of 4 valence electrons in carbon atoms. Then the mirror image of A can be drawn to form structure B. Answer Verified 286.2k + views Hint: Use tetravalency of Carbon atom to explain asymmetric carbon atom. If the bonding at C 2 of 2-butanol is drawn in three dimensions and this structure called A. Let's apply our chirality discussion to real molecules.Ĭonsider 2-butanol, drawn in two dimensions below.Ĭarbon #2 is a chiral center: it is sp 3-hybridized and tetrahedral (even though it is not drawn that way above), and the four substituents attached to is are different: a hydrogen (H), a methyl (-CH 3) group, an ethyl (-CH 2CH 3) group, and a hydroxyl (OH) group. We will begin to explore this last idea in later in this chapter, and see many examples throughout the remainder of our study of biological organic chemistry.īe aware - all of the following terms can be used to describe a chiral carbon.Ĭhiral carbon = asymmetric carbon = optically active carbon = stereo carbon = stereo center = chiral center However, enantiomers do differ in how they interact with polarized light (we will learn more about this soon) and they may also interact in very different ways with other chiral molecules - proteins, for example. Enantiomers have identical physical properties (melting point, boiling point, density, and so on). It should be self-evident that a chiral molecule will always have one (and only one) enantiomer: enantiomers come in pairs. Enantiomers are pairs of stereoisomers which are mirror images of each other: thus, A and B are enantiomers. It follows that B also is not superimposable on its mirror image (A), and thus it is also a chiral molecule.Ī and B are called stereoisomers or optical isomers: molecules with the same molecular formula and the same bonding arrangement, but a different arrangement of atoms in space. Now, if we flip compound A over and try to superimpose it point for point on compound B, we find that we cannot do it: if we superimpose any two colored balls, then the other two are misaligned.Ī is not superimposable on its mirror image (B), thus by definition A is a chiral molecule. Notice that every point on A lines up through the mirror with the same point on B: in other words, if A looked in the mirror, it would see B looking back. The mirror image of A, which we will call B, is drawn on the right side of the figure, and an imaginary mirror is in the middle. The meaning of ASYMMETRIC CARBON ATOM is a carbon atom in union with four atoms or groups no two of which are alike, compounds containing such a carbon atom. Consider the molecule A below: a tetrahedral carbon, with four different substituents denoted by balls of four different colors. Since thalidomide has a stereogenic carbon atom, it exists as two enantiomers. Chiral molecules contain one or more chiral centers, which are almost always tetrahedral ( sp 3-hybridized) carbons with four different substituents. Enantiomerism the property of asymmetric molecules that look 'the same' but are actually mirror images of each other is one of the many topics, perhaps the most egregious, that drive organic chemistry students batst crazy. Certain organic molecules are chiral meaning that they are not superimposable on their mirror image. The term chiral, from the Greek work for 'hand', refers to anything which cannot be superimposed on its own mirror image.
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