Review Sheet for Chemistry 311 Exam Study all prelab, postlab and introduction questions. Besides topics covered in prelab, postlab and introduction questions Mechanisms SN1 and SN2 (specific to the reactions carried out and the formation of the precipitate) Esterification Dibenzalacetone synthesis Reduction Benzoin condensation (specifically the roles thiamine plays), where water and OHcame from in the mechanism Calculations Theoretical and % yield Percent recovery for recrystallization Partition Coefficient for Extraction – single and multiple extractions Raoult's Law for Distillation Balanced equations of: Reactions that occured in acid-base extraction all synthesis (major products) all side products from synthesis all intermediates in the synthesis all reactions (stepwise) that occur during the synthesis (This are for experiments where the reaction happens in two or more steps – indicated by addition of a reactant or observation) Structures and names of all starting materials, products and side-products for all synthesis Safety rules and regulations - clothing and safety attire, eye protection, contact lenses, do’s and don’ts - treatments for chemical on parts of the body, the eye (including do’s and don’ts) - treatments for burning clothing (including do’s and don’ts) - remedy for burning reagents (including do’s and don’ts) Modifications provided in "hints for preparation" to help reactions proceed smoother. All sketches of apparatus (label with appropriate names from pg 10). Be able to draw the apparatus. Functions of parts of the apparatus. Placement of all parts of apparatus with relation to other parts– why should certain parts be placed in a certain manner. You should be able to tell if an apparatus is set up correctly or not. Melting Points Why are melting points carried out? Definition of the melting point of a pure compound. What is the criteria for impurity?
What forces affect melting point? (Also, consider the effect on the melting point of larger molecules, symmetrical molecules and R,S isomers, and hydrogen bonding molecules) Define eutectic point (two ways mentioned in notes) and eutectic temperature Melting point composition graph Mixed melting points experiment How sample is prepared? Why sample should be prepared in a specific manner? Criteria for sample before packing and how it should be packed. How should sample be heated and why? What may happen if you heat the sample too quickly? Definition of melting range Why does sample shrink before melting What happens if you have too much sample What happens if sample is coarse (not powdered) Recrystallization Reason for carrying out Picking solvent: like dissolves like Requirements for solvents with respect to solute and impurities Requirement for solvents for solvent pairs Why solvent pairs are used How to minimize loss of product in crystallization, collecting and washing steps – why does product get lost in these steps Requirements when cooling Remedies for unsaturated solution, supersaturation Definition of superheating and prevention – how boiling sticks and stones achieve their purpose. Why crystals oil out – remedies and prevention Small powdery crystals – why they form and how to prevent, why large crystals are preferred Activated charcoal – purpose and how it works Why is it important that boiling stick is removed during cooling process? Extraction Reason for carrying out Flowchart on how to separate strong acids, weak acids, bases and neutral compounds Why extractions are carried out in the sequence they are (weak base then strong base) Reactions of the acid-base extractions Requirements for extraction solvents Emulsions – definition, causes, and remedies How to decrease solubility of organic substance in aqueous layer Why drying agent was used? What observations indicate that an organic layer is dry? You must know what substance(s) you have used as a drying agent in the experiments you have carried out. Criteria for choosing drying agent How do you ensure all product is transferred from drying agent Advantages of t-butylmethyl ether and disadvantages of diethyl ether Why don’t you get 100% recovery? TLC
Precautions to take when spotting, developing and visualizing Why should bores of capillaries be small Characteristics of solvents that allow them to migrate rapidly Adsorbent materials and specific uses (what kind of adsorbents would be better for what kind of substances) Table 9.2 (Order of solute migration) Uses of TLC and how it is used– all 6 Effects of using too polar or too nonpolar a solvent Distillation Reason for carrying out Insulation of apparatus Wrapping with a wet paper towel – why? Position of the thermometer Position of end of sidearm Boiling point composition graph – Fig. 5.2 and 5.4 – phases in the graph and how to interpret data from the graph (liquid and vapor composition of mixture) Uses of simple and fractional distillation – what kinds of mixtures are suitable for each kind of distillation Behavior of temperature during a simple or fractional distillation of a mixture. Definition of azeotrope (minimum and maximum) – recognize azeotrope on boiling point composition graph Boiling points of miscible and immiscible mixtures with relation to pure compounds Definition of hold up Use of a packing material and criteria for choosing Steam distillation – uses, what kind of mixture used in steam distillation - difference between vacuum distillation and steam distillation What requirement is necessary for boiling point in steam distillation to be constant? Precautions about distilling to dryness, distilling in closed system. Sources of error in a distillation Nucleophilic Substitution Factors that affect SN1 and SN2 (general and specific to experiments carried out) -structure of alkyl halides, temperatures, solvents, leaving groups, etc. (also know why trends are the way they are) - relative rates of reactions and the reason for those relative rates. - the importance of using the exact same amount of alkyl halide and nucleophile in each test tube - possibility of a false positive in a reaction - why vinyl and aryl halides don’t undergo SN1 or SN2 - products when starting alkyl halide is chiral and why. - why do the Br- and Cl- not attack the alkyl iodides that form in the SN2 reaction carried out? Esterification How Le Chatelier principle could be used in this reaction (both methods) - why was one used and not the other? How water could be removed? (both methods) -why was one used and not the other? Why was apparatus set up the way it was? (on an angle, wrapping the condensor with wet paper towel etc) Role of each step of the reaction (including the simple distillation that was asked for in the procedure but not carried out)
Purpose of IR and interpretation of IR spectrum Role of resin and advantages Disadvantages of using traditional acid catalyst and purpose for each of the steps needed to be carried out if traditional acid catalyst is used Catalytic acid Sources of error Reasons reaction may not go to completion Reduction How reduction is characterized in organic chemistry Why NaBH4 used instead of LiAlH4 Why was ethanol used as solvent instead of ether Why was excess NaBH4 used in the reaction Specific side products and why they form Role of each addition of water Role of ice bath Why recrystallization carried out Sources of error Dibenzalacetone synthesis Specific side products and why they form Mixed aldol – drawback and how to minimize mixture of products Role of sodium hydroxide Role of water and its source Reason for washing crystals with water, what may happen if you don’t Why recrystallization carried out Where each species that carries out a specific step in the mechanism originates Ease of water leaving – why Requirements for starting materials for aldol addition and condensation Formation of enolate (why it occurs) Catalytic base Sources of error Benzoin condensation Advantage and disadvantage of thiamine catalyst differences between benzoin and aldol condensation – product and starting material Why two moles of hydroxide ion necessary Why TLC used Why recrystallization might have been carried out Sources of error.