1. Introduction to Organic Chemistry

2. Introduction toOrganic Chemistry There are two main areas for this chapter: 1. Structure & Nomenclature 2. Isomerism 3. DrawingOrganic Structures -Drawing displayed formula or full structural formula is often tested. Be sensitive to these terms. Students often forget to illustrate bonds in substituents (e.g. OH and NH2) when asked to draw displayed formula:wrongcorrect 4. DrawingOrganic Structures -When drawing structural formulae, it is a good practice to illustrate the trigonal planar arrangement about sp 2 C (i.e. C=C):H3CCl CHC CH3 5. Isomerism -An easy way to distinguish between structural and stereoisomers is: Stereoisomers have the same name Structural isomers have different names 6. Structural Isomers Q: Is there a mathematical formula to calculate the number of structural isomers? A: No. You have to draw out all possible structures. But there is a general approach to doing that. 7. DrawingStructural Isomers 1. Draw the structure with the longest possible chain. 2. If a functional group is present, shift the position of the functional group to get all the different isomers 8. DrawingStructural Isomers 3. After all positional isomers have been identified, draw the structure of the next longest chain (minus 1 C) 4. Shift the position of the functional group and/ or substituent to get all the different isomers 5. Repeat steps 3 & 4 until no more variations 9. Stereoisomers - When using the formula 2n to determine the number of stereoisomers, note that n = number of stereogenic centers (i.e. chiral C + C=C that can exhibit cis/trans) - Students make mistakes when they blindly count the total number of C=C 10. Stereoisomers - Note that C=C within a cyclic ring cannot exhibit cis-trans 11. Stereoisomers Q: How many stereoisomers are there for retinol (Vitamin A)? 12. Stereoisomers A: no. of chiral C = 0 no. of C=C that can exhibit cis/trans = 4 no. of stereoisomers = 24 = 16C=C in a ring cannot exhibit cis/trans 13. IdentifyingChiral Carbons Tip 1: Ignore Cs in double bonds - they have only 3 neighbours Tip 2: Ignore Cs in benzene ring - they are all C=C Tip 3: Ignore V-shaped Cs - they are bonded to 2H (same groups) 14. IdentifyingChiral Carbons Tip 4: Look for Cs that look like:peaceclaw 15. IdentifyingChiral Carbons 1. Look for peace and claw carbons 2. Check if there are 4 different groups on each of these carbons. 16. IdentifyingChiral Carbons Q: How to check if a C in a cyclic ring has groups? e.g.different 17. IdentifyingChiral Carbons - Draw a line bisecting the C and the two groups in question. - If the structure is symmetrical about the line, the two groups are the same and vice versa. 18. IdentifyingChiral Carbons Check groups 1 & 2:4 132not symmetrical groups 1 & 2 are different 19. IdentifyingChiral Carbons Check groups 1 & 3:4 132not symmetrical groups 1 & 3 are different 20. IdentifyingChiral Carbons Check groups 2 & 3:4 132not symmetrical groups 2 & 3 are different all 4 groups are different C is chiral 21. DrawingOptical Isomers 1. Draw the tetrahedral structure about the chiral C 2. Fill in the four different groups with the most complicated group at the top - this will help to avoid issues with reflecting about the mirror plane. 22. DrawingOptical Isomers most complicated group CH2CH(CH3)CH2CH2CH3ClCH2CH(CH3)CH2CH2CH3Cl 23. DrawingOptical Isomers Error 1: Did not show tetrahedral arrangement CH2CH3 HC ClCH3CH2CH3 H3CC ClH 24. DrawingOptical Isomers Error 2: C* not bonded to C 25. DrawingOptical Isomers Error 3: Reflecting groups i.e. H3CH2CH2C 26. Functional Groups - When identifying functional groups, it is safer to name the homologous series (i.e. alkene, benzene, aldehyde, ketone etc). - Using terms like carbonyl may sometimes be ambiguous. - Alkane is not a functional group 27. Functional Groups - When smaller functional groups make up a larger functional group, you should name the larger one: i.e. phenol (instead of benzene or alcohol) carboxylic acid (instead of alcohol) Examplecarboxylic acidcorrectalcoholwrong