Chem 241a-1st Edition Lecture 8 Outline of Last Lecture I. Continuation of chair conformers of cyclohexanesII. Stereochemistry (Chapter 5)a. Chiralb. AchiralIII. EnantiomersIV. DiastereoimersOutline of Current Lecture I. Naming Chiral Centers – R+S formalismII. Determining Number of StereoisomersIII. Properties of StereoisomersCurrent LectureIntro: How can we differentiate different chiral molecules, especially those that look similar?For example: These molecules look very similar butcannot be superimposed on one another (chiral) – sohow can we classify them?I. Naming Chiral Centers – R+S formalismThere are two names that we can give to the chiral centers of a molecule that is determined by the groups attached, R and S. So how do we distinguish the two?a. Prioritize the groups (1-4) using Chan-Ingold-Prelog Rules:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. The immediate atom attached to the carbon with the highest atomic number gets first priority, and so on. (Note: Typically the 4th priority is Hydrogen because it’s only an atomic number of 1)Ex: In this group, the OH has the highest priority because Oxygen has an atomic number of 6, nitrogen has an atomic numberof 5, and Carbon has an atomic number of 4. The 4thpriority belongs to hydrogen, which is not picturedii. If we are comparing chiral centers that have thesame directly bonded atom, then we look for thehighest atomic number on the first point ofdifference (POD)Ex: This chiral center has three carbons and a hydrogen attached to it, so how do we determine which one is the highest priority?We can write out the groups on each of the carbons(what each is attached to): The topmost c [H,H,H]The middle c [C,H,H]The bottom c [C,C,H]So the first POD is between the top carbon’s H with theother two C’s, so we know that the topmost carbon is second to last priority compared to the 4th priority of HydrogenThe second POD comes from the middle H and the bottom C. So we knowthat the bottom carbon has the highest priority, and the middle carbon has the second priority, as pictured.iii. If groups have double and triple bonds, those bonds are counted twice and three times, respectivelySo, when we write out what is bonded to each carbon, the right carbon is [C,C,H];This right carbon is [C,C,C]And this Carbon is [O,O,O]b. After you determine the priorities, take priority group 4 and put it in the back (away from the eyes)c. Look at the order of the 1-3 priorities in a circle; if the order is clockwise, it is an R formation; if the order is counter clockwise, it is an S formationd. Note: anytime we deal with an enantiomer, the S/R conformation switches to R/S conformationII. Properties of Stereoisomersa. The maximum number of stereoisomers that any one compounds can have is 2n, where n is the number of chiral groups in the moleculei. 1 chiral group = 2 stereoisomersii. 2 chiral groups = 4 stereoisomersiii. 3 chiral groups = 8 stereoisomers and so onEx: In thisexample, there is astereoisomer for both the cis and trans version of this molecule, making a total of four stereoisomers for the same moleculeb. Some molecules have less than the max, however, due to symmetry in the molecules (and have one less stereoisomer)i. These molecules are called meso molecules because they are achiral molecules with chiral centers and are mirror images with symmetryc. Properties of Stereoisomersi. Diastereomers-different compounds can be identified by simple lab techniques because they have different physical properties (such as bp, mp, Rf value, etc)ii. Enatiomers-they have the same physical properties and are hard to