ORGANIC - BRUICE 8E CH.3 - AN INTRODUCTION TO ORGANIC COMPOUNDS

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2 CONCEPT: INDEX OF HYDROGEN DEFICIENCY (STRUCTURAL) A saturated molecule is any molecule that has the maximum number of hydrogens possible for its chemical structure. The rule that we use for this is. Any molecule that has less than number of hydrogens is considered to be. EXAMPLE: How many hydrogens must the following carbon skeletons contain to be saturated? Are they missing any? IHD rules give us the ability to quickly determine which molecules are more saturated and which molecules are less saturated with hydrogen. 1 IHD = Compound is missing hydrogens. Rings/Double bonds = Triple Bonds = EXAMPLE: What is the degree of unsaturation of the following compounds? Page 2

3 CONCEPT: INDEX OF HYDROGEN DEFICIENCY (MOLECULAR FORMULA) Molecular Formula: - When given only the molecular formula of the molecule use the following rules. (Theoretical # H s Actual # H s) / 2 = IHD, where: H / X = O = N = EXAMPLE: What is the IHD for each of the following compounds? a. C4H7Cl b. C6H7N c. C7H12O2 Page 3

4 CONCEPT: CONSTITUTIONAL ISOMERS Constitutional isomers are molecules that have identical molecular formulas (all the same atoms), but have different. You will be asked to compare molecules and determine how they are related. EXAMPLE: How are the following two compounds related? A) Identical Compounds B) Constitutional Isomers C) Different Compounds Steps to solve Constitutional Isomer Problems: Step 1. (Are the atoms all the same?) Count non- atoms and IHD in both compounds - If not exactly the same, they are - If the same, then go to step 2 Step 2. (Are the atoms all connected the same?) Look for a atom, then count bonds from there. -If not exactly the same, they are -If the same, then they are EXAMPLE: How are the following sets of compounds related? A) Identical Compounds A) Identical Compounds B) Constitutional Isomers B) Constitutional Isomers C) Different Compounds C) Different Compounds Page 4

5 CONCEPT: FUNCTIONAL GROUPS We can group several millions of different molecules into subsets of similar 1. Hydrocarbons All carbon groups regardless of size can be symbolized using an group. When an alkane is attached to a greater carbon chain, it is given an suffix. (i.e. group) Carbons are given a degree based on how many other they are attached to Hydrogens possess the degree as the carbon they are attached to Degrees are expressed as primary, secondary, tertiary and quaternary (1⁰, 2⁰, 3⁰, 4⁰) EXAMPLE: Determine the degree of the indicated carbons and hydrogens Page 5

6 2. Alkyl Halide Any R group directly attached to a halogen. The degree of alkyl halide is determined the same way as The carbonyl is NOT a functional group, but it is a major component of many functional groups 3. Alcohol 6. Carboxylic Acid ( ) Degree of alcohol is determined the same The acid of organic chemistry way as 4. Amine 7. Amide ( ) Degree of alcohol is determined the same Degree of alcohol is determined the same way as. way as. 5. Ether 8. Ester ( ) Page 6

7 9. Carbonyls The term carbonyl is not the proper name of the functional groups because the functionality of the group depends on its location on the carbon chain.. Ketone ( ) Aldehyde ( ) - carbonyl group - carbonyl group 10. Nitrile 11. Benzene Directly attached to R group ( )( ) Extra CH2 between R group ( )( ) EXAMPLE: Identify all the functional groups in the following compound. Show degrees where applicable. Page 7

8 12. Other Carbonyl Compounds Acyl Chloride ( ) Anhydride ( ) 13. Sulfur Compounds Page 8

9 PRACTICE: Identify all the functional groups in the following compound. Show degrees where applicable. a. b. c. Page 9

10 CONCEPT: ALKANE NOMENCLATURE Before 1919, chemists literally had to memorize thousands of random (common) chemical names. IUPAC naming provides a systematic method to give every chemical structure a unique, unambiguous chemical name. CONCEPT: ALKANE PREFIXES We will use the following set of rules to systemically name alkanes: Rule #1. Number the longest carbon chain and assign a root name accordingly. If there is a tie between longest chains, choose the chain that gives substituents. Alkane Prefixes Page 10

11 CONCEPT: ALKANE NOMENCLATURE Rule #2: Decide the direction of the root chain starting from the closest substituent If there is a tie between substituents, compare the substituents If there is STILL a tie, determine direction using. EXAMPLE: Name the longest carbon chain and determine the direction of the root chain EXAMPLE: Name the longest carbon chain and determine the direction of the root chain Page 11

12 CONCEPT: ALKANE NOMENCLATURE Rule #3: Designate numerical locations of substituents When one or more substituents are identical, use the prefixes (2), (3), (4). Represent substituents using yl suffix on alkane groups. (alkanes become alkyls) EXAMPLE: Name the root chain, determine the direction of the root chain and then identify & locate all substituents Rule #4: Name substituents in alphabetical order (prefixes don t count toward this!) Rule #5: Use to separate numbers from numbers, to separate letters from numbers. EXAMPLE: Provide the IUPAC name for the following alkane: Page 12

13 CONCEPT: COMMON SUBSTITUENTS Although we try to use IUPAC naming as much as we can, there are a few common substituents you should know the common names for: EXAMPLE: Name the following alkane: Page 13

14 CONCEPT: CYCLOALKANES Monocyclic compounds are named by attaching the prefix cyclo- to the root chain. The root is assigned to the portion of the alkane with the greater number of carbons: If there is only 1 substituent, the location can be. EXAMPLE: Name the following alkanes: Bicyclic compounds are composed of distinct rings attached along one bond. Bridged compounds are unique types of bicyclic molecules composed of compound rings attached by atoms. Page 14

15 CONCEPT: BICYCLICS Bicyclics come in different categories: Normal and Bridged. Nomenclature: A bridgehead atom must always be in the 1 position. Format: bicyclo[ring1.ring2.ring3]alkane Number from the largest ring to the smallest ring - If it has no bridge, then the third ring just counts as Page 15

16 CONCEPT: ALKYL HALIDES Alkyl halides are named by naming them as a substituent before the root chain and indicating their location. Prefixes: -F, -Cl -Br -I Alkyl halides have NO when it comes to numbering the direction of the chain. EXAMPLE: Name the following compounds: a. b. Page 16

17 CONCEPT: ALCOHOL NOMENCLATURE Alcohols are named by adding the modifier (- ) the end of the root. Alcohols receive priority in numbering alkanes Locations can be donated the root old school or the root new school EXAMPLE: Name the following compound: a. Page 17

18 CONCEPT: ETHER NOMENCLATURE Common Name: List alkyl groups in alphabetical order and follow with the word IUPAC: Smaller half of the ether is named as an substituent on the main alkane chain EXAMPLE: Provide the correct common and IUPAC name of the following ether Page 18

19 CONCEPT: AMINE NOMENCLATURE The degree of the amine directly determines how it will be named. 1 o Amines: Add the suffix amine is to the name of the alkyl substituent. If the alkyl substituent s name ends with an e replace it with amine. EXAMPLE: Name the following 1 o Amines. Page 19

20 If a higher priority functional group is present then the suffix amine changes into the prefix amino. EXAMPLE: Name the following multi-functional amine. 2 o and 3 o amines: If different alkyl groups are attached the largest alkyl group is chosen as the parent name, and the other alkyl groups are N-substituents. EXAMPLE: Name the following amines Page 20

21 CONCEPT: INTERMOLECULAR FORCES IMF s are what make molecules. Without them everything would be Boiling point / melting point questions are always directly referring to the strength of between molecules. 1. Hydrogen Bonding (H) Bound to small, highly electronegative atoms: 2. Dipole-dipole (net dipole force) 3. Van der Waals (London Dispersion Forces) Increase with: a. Size b. Ring > Chain > Branched Page 21

22 PRACTICE: Which of the following pairs of molecules would have the highest boiling point? 1. OR 2. OR 3. OR 4. OR Page 22

23 CONCEPT: SOLUBILITY Only one rule: dissolves EXAMPLE: PRACTICE: Circle the following molecules would you expect to be miscible in an aqueous solution? a. b. c. d. e. f. Page 23

24 CONCEPT: CONFORMATIONS Most organic molecules have the ability to exist in multiple arrangements without experiencing any chemical changes. Many of these arrangements exist due to the ability of bonds to These arrangements are NOT isomers because structurally the molecule never changes. EXAMPLE: Hexane Conformers These alternate arrangements are called PRACTICE: Determine if the following pairs of molecules are isomers or conformers. a. b. c. d. Page 24

25 CONCEPT: NEWMAN PROJECTIONS CONFORMATIONAL ENERGY Newman projections are drawings used to help us visualize all the conformers that can be made by rotating a bond The dihedral angle is used to describe rotation around a single bond Calculated by taking the angle of the largest group on the front and back relative to each other θ = = : The two largest groups overlap each other energy θ = = : The two largest groups are adjacent to each other energy θ = = : The two largest groups are opposite to each other energy EXAMPLE: Plot the following dihedral angle values with their respective energy to determine the energy diagram for the rotation of hexane along the C3 C4 bond. Page 25

26 CONCEPT: NEWMAN PROJECTIONS METHOD Through a series of steps, we can consistently draw accurate Newman Projections to determine conformational stability. EXAMPLE: Draw the most energetically favorable Newman Projection for CH3CH2CH2CH2CH3 down the C2 C3 bond. 1. Convert problem into bond line structure 2. Highlight the bond of interest 3. Draw an eyeball glaring down the length of the bond 4. Surround only the bond of interest with ALL implied hydrogens 5. Draw front carbon with 3 groups in the front and a back carbon with 3 groups in the back 6. Determine which dihedral angle would correspond Page 26

27 PRACTICE: DRAWING NEWMAN PROJECTIONS 1. Draw the most energetic Newman Projection of CH3CH(C6H5)CH3 2. Draw the most stable Newman Projection of CH3CH2CH2OH through the C2 C1 bond. Page 27

28 CONCEPT: CALCULATING CONFORMATIONAL ENERGY Sometimes we ll be asked to calculate the energy barrier (kj/mol) of rotation or of a specific interaction. Barrier to rotation can be calculated by memorizing other known values. EXAMPLE: The barrier to rotation for the following molecule is 22 kj/mol. Determine the energy cost associated with the eclipsing interaction between a bromine and hydrogen atom. PRACTICE: The barrier to rotation for 1,2-dibromopropane along the C1 C2 bond is 28 kj/mol. Determine the energy cost associated with the eclipsing dibromine interaction. Page 28

29 CONCEPT: HEAT OF COMBUSTION Heat of Combustion is a technique that blows up molecules to see how energetic they are: Heat of Combustion = Energy = Stability Heat of Combustion = Energy = Stability Sources of Alkane Instability: 1. Shape: Straight chains are less stable than branched chains. 2. Strain: Found in many cycloalkanes. There are a few types of strain: Angle strain exists when cyclic tetrahedral bonds are forced out of their ideal bond angle of Torsional strain exists when neighboring carbons possess hydrogens that overlap in space (eclipse) EXAMPLE: Which of the following conformations of cyclohexane would have the lowest heat of combustion? Page 29

30 CONCEPT: CYCLOHEXANE CHAIRS AND POSITIONS Although so far we have assumed rings to be planar, cyclohexane actually exists in a form to alleviate torsional and ring strain. Like single bonds, cyclohexane can to form two different chair conformations in equilibrium with each other Chair conformations have TWO substituent positions: Page 30

31 CONCEPT: CYCLOHEXANE - DETERMINATION OF CIS AND TRANS How to draw cyclohexane: Draw two slightly angled parallel lines Cap both ends Cis or trans is based on whether the groups are facing the same of the ring NOT based on whether they are axial or equatorial. EXAMPLE: Name the following cyclohexane compounds: a. b. Page 31

32 CONCEPT: CYCLOHEXANE EQUIVALENT CHAIRS Many of the cyclohexane molecules we will draw in this chapter will be substituted. In this chapter, only three things matter when drawing equivalent chairs. Distance between groups Cis vs. Trans Equatorial Preference (determines conformers) PRACTICE: Determine if the following pairs of chairs are identical, conformers or different. a. b. c. Page 32

33 CONCEPT: CYCLOHEXANE EQUATORIAL PREFERENCE One of the two positions is much more crowded or than the other. Rings will ALWAYS flip in order to accommodate the preference of their largest, bulkiest substituent. When chairs flip: Axials become Equatorials become EXAMPLE: This chair is not in its most stable conformation. Draw the chair flipping to accommodate equatorial preference a. Page 33

34 PRACTICE: Drawing Equatorial Preference 1. Draw the MOST STABLE conformation of cis-1-tert-butyl-4-methylcyclyhexane 2. Draw the LEAST STABLE conformation of trans-1-tert-butyl-3-neopentylcyclohexane. Page 34

35 CONCEPT: CALCULATING FLIP ENERGY Sometimes we ll be asked to calculate the energy required (kj/mol) to flip chairs into the axial position. PRACTICE: Calculate the difference in Gibbs free energy in (kj/mol) and (kcal/mol) between the alternative chair conformations of the following disubstituted cyclohexanes: a. trans-4-iodo-1-cyclohexanol b. cis-2-ethyl-1-phenylcyclohexane Page 35

36 CONCEPT: CALCULATING CHAIR EQUILIBRIUM We can use the difference in ( Gº) to calculate the percentage and/or ratio of chairs at any given temperature. First, use Gº to solve for the equilibrium constant: *Correction: Gas Constant = Then, use Ke to solve for the percentage of each conformer: PRACTICE: Estimate the equilibrium composition of the chair conformers of the following cyclohexanes at room temp: a) cis-1,3-diethylcyclohexane b) trans-1-methyl-3-phenylcyclohexane Page 36

37 CONCEPT: DECLINS Declins are specific types of bicyclic molecules. They come in two conformations of differing stability. EXAMPLE: Draw the following declin as a chair conformation in the most stable conformation. Page 37