Organic Lab Exam Review PDF

Lab Safety and Guidelines - For a chemical splash, you must use the eyewash station provided for at least 15 mins - Cover all violate chemicals with a beaker or a watch glass - Corrosive chemicals: - Substances that cause visible destruction or permanent changes in human skin tis...

Lab Safety and Guidelines - For a chemical splash, you must use the eyewash station provided for at least 15 mins - Cover all violate chemicals with a beaker or a watch glass - Corrosive chemicals: - Substances that cause visible destruction or permanent changes in human skin tissue at the site of contact/ main classes include strong acids/bases and dehydrating agents - Immediately flush contaminated area with copious amounts of water - Flammable Liquids: - Chemicals that have a flash point below 100 F - If there is a spill: - Remove and turn off all sources of ignition - Are best removed through the use of spill pads - All used absorbent materials should be placed in heavy duty poly-bags which are sealed, labeled, and disposed - Disposing of excess acids/bases: - Neutralize any excess acid/base that you may be collecting by appropriately neutralizing it, check the pH paper and then pour it down the sink (Sodium bicarbonate is an example) - If there was organic solvent in the waste then it should not be poured down in the sink - Disposing of inorganic solid waste: - Inorganic solid waste (dry agents: CaCl2) can be disposed of into the biohazard waste boxes Lab A/B - Slides - An equivalent is the experimental ratio in which reactants are added to this reactions - Acetic anhydride and salicylic acid react in 1:1 ratio - Hydrolysis is base promoted, not base catalyzed because the base (OH-) is the nucleophile that adds to the ester and forms part of the product. It participated in the reaction and is not regenerated later - Hydrolysis of Triacylglycerols - Each triacylglycerol is a triester containing three long hydrocarbon side chains - Metabolism: Cleavage of three ester bonds forms Glycerol and three long chain-fatty acids - Hydrolysis of Lipid is the same as Hydrolysis of and ester Hydrolysis - Catalyzed by the enzyme lipases - Stoichiometry Review - Theoretical yield: The yield of reaction assuming 100% conversion of the limiting reactant to the product - Limiting reagent: The reactant that is present int he smallest amount and would limit the amount of product possible. The moles of product is determined by the moles of “Limiting reactant: on a molar equiv basis - Percent yield: is calculated based on the amount of products actually obtained in the experiment and the Theoretical yield: % yield = actual yield / theoretical yield * 100  - Multistep synthesis: The overall percent yield is determined by multiplying the yield of each step expressed as a decimal - Recrystallization - Purify a solid organic compound by using a stable solvent - Rule for selecting good solvent for recrystallization - The solid that you are trying to purify should be soluble int he hot solvent and insoluble in a cold/room temperature solvent - Vacuum filtration technique - Tech that is used to quickly and completely separate a solid from the liquid in which it is mixed - Tech. to keep in mind: - Direction of the ring stand (front facing) - Vacuum filter flask is firmly clamped - to prevent from tipping over - Uses an adapter to ensure a tight sequel between Buchner funnel and vacuum filter flask - Employs Heavy-walled rubber tubing - to prevent the tubing from collapsing from atmospheric pressure on the outside when the vacuum is applied. - Lab C - Slides - Miscible liquid pairs (acetone and water) are not suitable for extraction - Must have two immiscible liquids to carry out a liquid - liquid extraction - Extraction - a technique used for the isolation and purification of organic compounds (Separatory funnel) - Theory of extraction- always better to do several smaller extractions than one big one to maximize amount of material extracted and to increase the theoretical recovery - Ring clamp always attached to the ring stand for support in the separatory funnel/ use adding solutions using a pyrex funnel (125 mL funnel and 19 width/22 length in mm standard taper joint - Pressure can build up in the funnel due to formation of carbon dioxide/ always vent funnel inside the fume hood and point towards the back of the hood/ when draining remove glass stopper or it will not drain - Typical solvent mixture - Non-polar organic + polar aqueous - Most dense solvent: sinks to the bottom (aqueous layer) - Less dense solvent: floats to the top (organic layer) - Extraction Technique - Compounds partition between two layers- based on relative solubilities - Forces that control solubility- Van der Waals forces/Dipole - Dipole forces/ Hydrogen bonding - Like dissolves like - oil and water do not mix - Reaction mixtures can be separated in this way (Salt and ionic species are present in water layer & Most organic compounds in organic layer)  - Drying with anhydrous inorganic salts (drying agents)/ combines water in the product and retains it as water of crystallization/ becomes free floating after enough is added Lab D: TLC - Slides - Chromatography “Color Writing” - Used as a qualitative analytical tool/simples economical method for separation of components/helps in following progress of a chemical reaction and effectiveness of a purification and conditions of macroscopic separations/ no restrictions on sample type- organic/ inorganic/ biological or medical/ highly sensitive - Types of Chromatographic Methods 1. TLC - Thin Layer Chromatography 2. LC - Liquid Chromatography (SP - Silica gel or Alumina; MP- a liquid) 3. HPLC - High Performance Liquid Chromatography (ultilze high pressure exerted by mechanical pumps to force the mobile phase through a very small diameter column packing that contains the stationary phase) 4. GC - Gas Chromatography (MP - a gas) - Silica Gel - most commonly used, inexpensive stationary phase - Extended covalent network of tetrahedral Si atoms bridged by “O” atoms - terminating in very polar Silanol (Si - OH) groups which creates a polar surface (CaSO4 helps silica gel binds to a plate) - Presence of OH groups created high polar energy - If reaction were to occur with only stationary phase then only the highly polar molecules would interact with the polar Si-OH bones which results in the slow movement of the TLC plate while quicker molecules is the result for less polar molecules because they hold less tightly to the Si-OH polars - Analysis of Thin Layer Chromatogram - Ratio to the front (Rf)/ Ration or distances or Retention Factor: - Rf = distance traveled by solute/ distance traveled by solvent - More polar/shorter distance traveled by the TLC - Less polar/ longer distance traveled by the TLC - Always spot on rough side/ spot lightly to avoid making a break in the silica gel coating which will hamper the separation Lab E: Diels-Alder Reaction - Slides - Cycloaddition reaction - A 1,4- addition of a 1,3-diene (conjugated diene) and an alkene (dienophile) to form a new six membered ring - Characteristics of a Diels-Alder Reaction 1. Thermal cycloaddition reaction 2. Concerted reaction 3. Three pi bonds break 4. Two new C-C sigma bonds and one new pi bond are formed in the product 5. Forms new six-membered rings  - Diene Reactivity: Can only react in the s-cis conformation (diene becomes unusually reactive)/unreactive in the s-trans conformation - Dienophile Reactivity: Electron withdrawing groups makes the dienophile more electrophilic (more reactive) - We do not use 1,3-butadiene directly as it is a gas that requires the usage of special lab equipments not used in the lab which is why butadiene sulfone is used instead to generate 1,3-butadiene within the flask - Xylene is used as the heat which drives the reaction forward - Cis-dienophile forms cis-subsituted cyclohexene/Trans-dienophile forms a trans-substituted cyclohexene - CHWR(Chilled water return)(top): Water flows out the condenser/ CHWS(Chilled water supply)(bottom): Water flows into the condenser - Refluxing the Reaction - Purpose: To heat a reaction mixture at its boiling temp to form the product without losing any material inside the reaction flask - Adv: Maintains a constant temp in the reaction flask/ reaction is able to reach equilibrium with minimal evaporation of material inside the reaction flask - Adv of using 3-Sulfolene 1. Non-hygroscopic solid 2. Not a flammability hazard 3. Excess 1,3 butadiene and SO2 are gasses at room temp and are distilled out during reflux Lab F: Fisher Esterification Reaction - Slides - Refluxing the reaction - Purpose: to heat the reaction mixture at its boiling temperature (of the solvent/excess reactant) to form the product without losing any material inside the reaction flask - Adv: Maintains a constant temp./ reaction reaches equilibrium with minimal evaporation of material inside the reaction flask - Purification techniques - Recrystallization/ Thin Layer Chromatography/ Extraction - For liquids: Simple distillation - Used to separate two liquids where the bp differ by greater than 100 oC at 1 atm/ must be miscible in each other - A technique where a liquid is vaporized by heating to its bp, then re-condensed back to a liquid (distillate) which is collected in a receiving flask - Vacuum Distillation - Used for compounds that either boil at too high of a temperature or that decompose near their boiling point - Under vacuum- compounds can be distilled at temperature lower than their atmospheric bp  - Only feasible solution for distilling compounds with BPs > 200 oC - Fractional Distillation - Used to separate liquid mixtures where the diff in bp in less than 100 oC at 1 atm - Fractionating column (Vigreux column) is inserted between the 3-way distillation adapter and the round bottom flask (distillation flask)- providing a larger SA over which a number of separate liquid-vapor equilibria can occur - Many vaporizations and condensations take place before the distiller is collected - Efficiency of a fractionating column - expressed by number of theoretical plates - We don’t use fractionating distillation because we actually want the product - One Theoretical plate: Equiv to one simple distillation cycle - Factors affecting BP: - Size (molecular weight) - Intermolecular Interactions - Waste Disposal - Red Sharps: All glass - Biohazard: gloves, paper towels - Silica goes in powder waste (inhalation hazard) - Acetone goes in non halogenated unless they were used to clean DCM - 10% Ethanol DCM = most polar - everything elutes - DCM alone = nonpolar - nothing elutes IR Spectroscopy - An Infrared Spectrum - IR Spectroscopy- primary used to detect functional groups present - IR Absorptions: arise due to stretching and bending of covalent bonds in molecules - 100% transmittance = all light shone is transmitted, none absorbed - 0% transmittance = none of the light shone is transmitted, all is absorbed - The functional group (diagnostic region) - determines the functional group present - The fingerprint region - used for structure elucidation by spectral comparison - Wavenumber is proportional to frequency (v) - Wavenumber is inversely proportional to wavelength ( - Infrared Spectroscopy - IR absorption: Four regions of the IR NMR Spectroscopy - Nuclear Magnetic Resonance - Nuclei possess charge and can spin - Spinning charges generate a magnetic dipole - Magnetic Dipoles: characterized by nuclear magnetic spin quantum number “I” - Three Cases of “I”  1. I = 0 a. Have an even number of protons/neutrons b. Do not spin- hence do not interact with applied magnetic field i. 12C, 16O 2. I = ½ a. Nuclei are NMR visible examples: 1H, 13C (non-radioactive isotopes of C, 1.06% natural abundance) 3. I > ½ a. Examples, 2H and 14N- difficult to observe - More nuclei are aligned with the externally applied magnetic field or the lower energy a-spin state - Delta E: Energy difference between a and b-spin states - Increasing the applied magnetic field = increasing delta E between spin states - Nuclei can absorb energy and flip from the a-spin state to the b-spin state. When this happens, the nucleus is said to be in RESONANCE with the applied magnetic field, hence the term: “Nuclear Magnetic Resonance” - The difference in energy delta E between the two spin states corresponds to a frequency in the Radiofrequency region of the EM spectrum - Planck’s equation: deltaE = hv - Chemical shift: - Position of the peak: Frequency difference between the resonance observed for the nucleus and the resonance observed for the reference compound (usually TMS)