Chem 219 Unit 3 Exam Questions With 100% Correct Answers

Chem 219 Unit 3 Exam Questions With 100% Correct Answers Stereochemistry the study of the three-dimensional structure of molecules Stereoisomers Compounds with the same structural formula and connectivity but with a different 3D arrangement of the atoms in space. Enantiomers Stereoisomers that that are non-superimposable mirror images. Enantiomers have the same connectivity but different orientations (twist) of the four atoms or groups in 3D space. The two different forms of the chiral molecule (the "left-handed" form or a "right-handed" forms) How do the differences caused by steroisomers differ than the differences caused by constitutional isomers. While the structural differences between stereoisomers are more subtle than those between constitutional isomers, stereoisomerism is often responsible for significant differences in the chemical and physical properties of organic compounds, including the biochemical behavior of many compounds such as drug molecules, amino acids, carbohydrates, and nucleic acids. Several of the human senses, especially smell, are greatly affected by stereoisomerism in organic compounds. cis-stereoisomers have the substituents on the same side/face of the ring or double bond trans-stereoisomers have the substituents on opposite sides/faces of the ring or double bond Chirality the concept of "handedness" in an object. Consider the difference between a pair of socks and a pair of gloves. A sock can be worn (interchangeably) on either the left or right foot, but the same is not true for the gloves. A left-handed glove cannot be worn on the right hand and vice-versa. The gloves possess the property of "handedness" (chirality) Observation will reveal that chiral objects are typically not symmetrical (asymmetric), while achiral objects typically exhibit multiple planes of symmetry within the object itself. chiral a molecule that is not superimposable on its mirror image (possesses the property of handedness) achiral A molecule that is superimposable on its mirror image (does not possess the property of handedness) What test can be applied to determine if an object is chiral or achiral? A simple test involves comparing the object and its mirror image for superimposability. Superimposability The ability to align (overlap) two objects so that every unique part of each is in direct alignment with the same unique part on the other. What does it mean when a molecule is a chiral molecule? An organic compound that can exist as two different forms ("left-handed" form or a "right-handed" form) Is lactic acid structure chiral or achiral? Attempting to superimpose lactic acid and its mirror image reveals that the two forms cannot be superimposed, and thus, the molecule is chiral, and it exists as two separate forms known as enantiomers (Figure 3.4). No matter how one of the structures is rotated, it is impossible to get all of the atoms/groups in one to align with the same atoms/groups in the mirror image structure. Is the molecule 2-chloropropane chiral or achiral? When the 3D structure of this molecule is drawn, a tetrahedral geometry is observed around the central carbon, similar to that of lactic acid. At first glance, it may not be clear that the molecule is achiral. It is only through the application of the superimposability test that the molecule reveals its achiral nature. The absence of a stereocenter is the reason why molecules like 2-chloropropane are achiral. An analysis of the 3D structure of 2-chloropropane reveals a tetrahedral geometry around the central carbon but only three different types of atoms or groups attached (there were 4 bonds to the carbon but 2 of the groups were identical). The symmetrical nature of the 2-chloropropane molecule comes from having two of the same group on the central carbon - this allows the structure to be superimposed on its own mirror image, and thus, makes the molecule achiral.