Ochem lab final notes - Professor: Richard Hubbard PDF

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Professor: Richard Hubbard...

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Org 1 Lab Final Notes: 

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Lab 1: Recrystallization o Recrystallization: a technique used to purify organic solid compounds with the goal to dissolve and subsequently crystallize a pure substance from the solution. o Know the five steps of recrystallization: 1. Choose an appropriate solvent 2. Dissolve impure mixture into hot solvent 3. Remove insoluble impurities from solvent via filtration 4. Cool to crystallize pure compound from the solution 5. Isolate pure compound via suction filtration o Characteristics of a good solvent:  Target must be soluble in high temp  impurities soluble at room temp or insoluble at high temps  Must be chemically inert (non-reactive)  Low boiling point, or highly volatile o Impurities both broaden and depress a pure compounds melting point range. o If crystals do not immediately form, you can encourage crystallization by:  Scratching the inner wall of the flask with a stirring rod  Introduce a seed crystal  Ice bath o Eutectic point: The lowest possible melting point of a mixture of substances o 50:50 Mixed Melting Point was conducted to verify unknown Lab 2: Simple and Fraction Distillation o Distillation: process of separating the component substances from a liquid mixture by selective evaporation and condensation. o Two types of distillation:  Simple  Fractional o Separation is achieved based on the difference in boiling point of miscible (able to mix in all proportions) liquids. o o

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Simple vs. Fractional:  Simple distillation is useful for separating miscible liquids with significantly different boiling points (typically a difference ≥100 C)  Fractional distillation is used to separate miscible liquids with boiling points less than 100 C apart Fractionating column: A glass tube filled with tightly packed steel wool or glass beads added to the simple distillation apparatus to create fractional distillation. Fractional distillation is a simple distillation apparatus with a fractionating column added.  Effectiveness measured by its column length and the density of packing material  Fractioning column efficiency is measured by the number of theoretical plates.

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Azeotrope: A mixture of two or more liquids that form a constant boiling liquid of distinct proportions  Ex: Ethanol

Lab 3: Solid-Liquid Extraction: Isolating Trimyristin from Nutmeg o Solid-Liquid Extraction: Extraction of a compound from a solid using a liquid media; Separation depends on compound's solubility in the particular solvent. o Know structure of trimyristin**** o Two types of extraction:  Solid-Liquid  Liquid-Liquid o Trimyristin, a triglyceride of myristic acid, was extracted in this experiment o Reflux: Process of boiling reactants while continually cooling and condensing the vapor thereby returning it back to the boiling flask. (NO loss of solvent)  Reflux STARTS after the first drop of condensation  Needs boiling chips o Nutmeg is 20-25% trimyristin o Simple distillation was used to separate the trimyristin from the solvent o Solvents used:  Methylene Chloride: extraction solvent  Acetone: Rinse/wash flasks and crystal

1 mol trimyristin  3 mol myristic acid + 1 glycerol

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Lab 4: Thin Layer Chromatography o Thin-layer chromatography (TLC): a chromatography technique used to separate nonvolatile mixtures. o TLC is a separation based on:  A stationary phase  A mobile phase o TLC is primarily used for identifying individual components of a mixture and following the progress of a reaction. o Solid stationary phase: Silica gel, alumina o Mobile liquid phase: the low boiling point organic solvent (ethyl acetate with 0.5% acetic acid) o Visualized dark spots on plates with a UV light. o What is the effect of polarity in regard to TLC?  Polar compounds give strong interactions with polar stationary phase, so elutes slower up TLC plate.  the molecules that moved the most towards the top of the plate were the most nonpolar.  caffeine was always at the bottom, its super polar and got stuck on the stationary phase with the silica gel. o Measuring Rf values:

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Distance traveled by solute/distance traveled by solvent Distances traveled by solute that are close to solvent line (elute faster) are more attracted to mobile phase and therefore more non-polar in nature.  Shorter distances closer to origin line (elute slower) are more attracted to stationary phase and are more polar in nature.  SAME Rf DOES NOT MEAN SAME SUBSTANCE*** o What solvent system will you be using to dissolve the common analgesics (powder) in preparation for TLC spotting?  1:1 methylene chloride: methanol o The four analgesics studied were:  Acetaminophen  Acetylsalicylic Acid  Caffeine  Ibuprofen Lab 5: ChemDraw Lab Lab 6: Acid-Base Extraction o Acid-Base Extraction is a form of Liquid-Liquid Extraction, which is the separation of compounds based on their relative solubilities in two different immiscible liquids o Ways of liquid-liquid extraction:  an aqueous solvent-organic solvent  two organic solvents of differing densities/polarities o REVIEW FLOW CHART****

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Two types of liquid-liquid extraction:  Organic Solvent Extraction  Acid/Base Extraction Bases: Aliphatic and Aromatic Amines Acids: Carboxylic acid (R-CO2H), Alcohols(R-OH), Phenols (Ar-OH), and Thoils(R-SH).

Basic component: Benzocaine Neutral component: diphenylmethanol Acidic components: benzoic acid, o-toluic acid, and 2-methoxybenzoic acid Methylene Chloride (CH2Cl2) is the organic/nonpolar solvent. Density determines layer; lightest on top (aqueous) and bottom layer (organic) LIKE DISSOLVES LIKE; meaning polar compounds are more soluble in polar solvents. Many organic compounds are nonpolar and therefore less soluble in polar solvents. o Amine in acidic conditions?  Deprotonated to form ammonium salt o Carboxylic acid in basic conditions?  Deprotonated to form carboxylate salt o Base and neutrals are insoluble in water o Know structures of compounds*** o Basic and neutral components are insoluble in NaOH because they do not combine to form water or water soluble salts Lab 7: Transfer Hydrogenation of Olive Oil o The addition of hydrogen (H2) to an alkene decreases the number of unsaturated carbon-carbon bonds while increasing the number of saturated bond o Oxidation: Increase the number of bonds to more electronegative elements and/or reduce the number of bonds to hydrogen o Reduction: Increase the number of bonds to hydrogen and/or decrease the number of bonds to more electronegative elements o Hydrogenation needs:  Catalyst (ex: Pd/C)  Hydrogen gas or alternative source of H2 o Hydrogenation of compounds using compounds that transfer molecular H2 o Provides a convenient and safe alternative to the use of flammable and explosive H2 gas o When cyclohexene is used as the hydrogen donor, the driving force of the reaction is the formation of benzene (highly stable aromatic ring) o o o o o o

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Cyclohexene was used as a source of hydrogen in this experiment The catalyst used was 10% Palladium on carbon (Pd/C) Benzene is the volatile liquid product of this reaction Hexane was used to wash product Celite was used to filter the catalyst from the reaction mixture after the reflux period.

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o Products are benzene and shortening** o REVIEW POST LAB QUESTIONS**** Lab 8: Preparation of Diphenylacetylene o Forming a carbon-carbon triple bond  Halogenation of an alkene, followed by double dehydrohalogenation

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Source of Br2 = Pyridinium hydrobromide perbromide AKA PHPB (KNOW STRUCTURE) Methanol was used to remove yellow tint from crystals Intermediate product is Stilbene dibromide (KNOW STRUCTURE) Solvent used in reflux  Ethylene glycol Final product: diphenylacetylene Balanced equation:

Lab 9: Gas Chromatography o Four factors that affect the compound separation obtained using gas chromatography:  Column length  Column temperature  Carrier gas flow rate  Stationary Liquid Phase o Compound to be purified must be volatile at high temps. o Retention time:

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The time that elapses from the introduction of the sample into the injection port until a component elutes from the column  Same retention time does not equal same compound  Compounds with short retention times move faster within the column; long retention times=slower movement within column. o Longer and wider columns give better separation (greater surface area) o Nucleophilic substitution generally occurs by two mechanisms: SN1 and SN2  SN1: Substitution Nucleophilic Unimolecular reaction  Unimolecular = one molecule in the transition state  occurs via an unstable carbocation intermediate [R3C+]  reaction occurs in several steps  SN2: Substitution Nucleophilic Bimolecular reaction  2nd Order Reaction: both reactants affect the reaction rate  Rate = k*[Nu]*[R-X]  k = reaction constant  [Nu], [RX] = concentration of nucleophile, alkyl halide o Single step reaction: bond breaking/forming happens simultaneously o In Substitution Reactions the nucleophile acts/substitutes as the leaving group. o Purpose of this lab: To determine which is a better nucleophile, Br or Cl  The bromide ion is a stronger nucleophile because it is bigger and more polarizable. o SN1, because tertiary Lab 10: Retro and Forward Diels-Alder Reactions o Formation of a new cyclohexene ring is achieved via a single, concerted step (no reaction intermediates). o Dienes must be oriented in an s-cis conformation, or else unreactive o Dienophiles are more reactive if they contain an electron withdrawing group adjacent to the carbon-carbon double bond o The presence of an electron withdrawing group also increases the yield and speed of the reaction o The stereochemistry of the dienophile is conserved during the course of the reaction o Four possible dienophiles (KNOW STRUCTURES):  DMAD: Dimethyl acetylenedicarboxylate  DEAD: Diethyl acetylenedicarboxylate  DPAD: Dipropyl acetylenedicarboxylate  DIAD: Diisopropyl acetylenedicarboxylate o Dimer: dicyclopentadiene o Cyclopentadiene used in reaction...