STRUCTURAL DRAWINGS 2D FRAMEWORK 1CARBON SKELETON 2FUNCTIONAL GPS 3LOCATION OF FGs 3D FRAMEWORK 1 RELATIVE STEREO 2 ABSOLUTE STEREO 3 CONFORMATIONAL FEATURES OK But what about:
VERIFYING OR CREATING STRUCTURAL DRAWINGS 1. A COMMON TASK 2. MANY ELEMENTS 3. STEREO STRUCTURES 4. CONCISE APPROACHES
FOUR TECHNIQUES NMR MS IR UV-VIS DESIRED OUTCOMES MOLECULAR FORMULA FUNCTIONAL GROUPS CH, CC, CZ, OR RINGS FUNCTIONAL GROUP POSITIONS REGIOCHEMISTRY STEREOCHEMISTRY 1)OBTAIN DATA 2)INTERPRET SPECTRA 4. CONCISE APPROACHES
REQUIREMENTS FOR A CONCISE APPROACH STEP-BY-STEP ANALYSIS UNDERSTANDING OF BASIC ORGANIC CHEM KNOW COMMON FUNCTIONAL GROUPS
REQUIREMENTS FOR A CONCISE APPROACH STEP-BY-STEP ANALYSIS KNOW STABLE VS. UNSTABLE STRUCTURES DEALING WITH ALTERNATIVES
3 TYPES OF PROBLEMS COMMERCIAL SAMPLES - VERIFYING THE LABEL SYNTHETIC REACTION PRODUCT - VERIFYING THE COURSE OF A REACTION UNKNOWN NATURAL PRODUCT - ESTABLISHING A NEW CHEMOTYPE -MOST DIFFICULT TYPE OF APPLICATION -O.S.A. PRINCIPLES & BIOGENETIC, TAXONOMIC ASSUMPTIONS
USES OF MOLECULAR FORMULA OR PARTIAL FORMULA UNSATURATION NUMBER (UN) OR DOUBLE BOND EQUIVALENTS (DBE) C n H 2n+2 ADD H FOR EACH X ADD CH FOR EACH N OR P EXAMPLES UN = 1 C 6 H 12 O EVEN H COUNT C 6 H 11 Cl ODD H COUNT C 6 H 13 N ODD H COUNT C 6 H 14 N 2 EVEN H COUNT
USES OF MOLECULAR FORMULA OR PARTIAL FORMULA UNSATURATION NUMBER & FUNCTIONAL GROUP CATEGORIES SELECTED EXAMPLES UN = 0 C-C NOT A FUNCTIONAL GROUP UN = 1 RING, ALKENE, CARBONYL, IMINE, NITRO UN = 2TWO RINGS, POLYENE, CUMULENE, ALKYNE NITRILE, ISONITRILE, ANHYDRIDE UN = 3NON-BENZENOID AROMATICS UN = 4ARENE, PYRIDINE
UN = [(2a+2) – (b-d+e)] 2 C 2 H 3 O 2 Cl = (4+2)-3-1 2 = 1 CaHbOcNdXeCaHbOcNdXe Unsaturation number/Double bond equivalents
This is the sum of the number of multiple bonds of all kinds kinds (C=C, C C, C=O, C=N, C N, N=O, etc) and rings in a molecule, and is extremely useful in structure determination. A double bond has a dbe = 1, a triple bond has a dbe = 2, and a benzene ring has a dbe = 4 (three double bonds plus one ring) Halogens count as hydrogen for this purpose. The number of oxygen atoms is immaterial. If you can identify securely by spectroscopic or other means the number of multiply bonded functional groups, e.g. carbonyl, present, the remainder will be rings. It is therefore possible to decide if the compound is acyclic, monocyclic, bicyclic, etc. and this is extremely helpful in imagining a structure. Once you have obtained the molecular formula, the first step in a structure determination is to work out the dbe.
NOW THE QUESTION HOW MANY STRUCTURES FIT C 2 H 3 O 2 Cl ?
Coupling/Splitting Two nuclei placed close together in the same molecule will interact and the NMR lines will be split into several components. The splitting is also referred to as coupling and the resultant splitting or coupling patterns are also called multiplets. The distance between the members of each multiplet in Hz is the coupling constant J, and can be calculated from the spectrum: J (Hz) = (ppm) x spectrometer frequency in MHz The proton proton interaction is transmitted through the intervening (s) electrons making up the chemical bonds, so the magnitude of J is an indication of the number and type of bonds.
Coupling/Splitting No coupling Coupling aa bb J ab
FACTORS CONTROLLING J’s 1)# OF INTERVENING BONDS (1,2,3,4, etc) 2)e - DENSITY 3)ANGLE H-C-C H-C-C-H H-C-C-C H-C-C-C-H 4)BOND HYBRIDIZATION 5)ELECTRONEGATIVTY OF ATOMS ALONG PATH
DETERMINING MOLECULAR FORMULAE FROM THE MOLECULAR ION Low resolution mass spectrum: 136 m/z
DETERMINING MOLECULAR FORMULAE FROM THE MOLECULAR ION Rule of 13: CH = 13 amu. Most common unit in organic compounds: Therefore (CH) 10 H 6 = C 10 H 16 Use CH 4 = H 16 = O CH 2 = H 14 = N H 12 = C
DETERMINING MOLECULAR FORMULAE FROM THE MOLECULAR ION Possible Formulae dbeAccurate mass C 10 H 16 3136.1248 C 9 H 12 O4136.0885 C8H8O2C8H8O2 5136.0522 C7H4O3C7H4O3 6136.0159 C 9 H 14 N3.5136.1123 C 8 H 12 N 2 4136.0998
DETERMINING MOLECULAR FORMULAE FROM THE MOLECULAR ION Experimental accurate mass measurement (from MS) was 136.1256 suggesting C 10 H 16 is the correct formula. The error between calculated and experimental mass is: 136.1256 - 136.1248 = 0.0008 = 0.8 mmu
Using DEPT 135 in conjunction with MS data to determine the MF Accurate mass (exp) 100.00891; (calc) 100.0885