Ochem lab 2 test1 review

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Feb 20, 2024

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Organic Chemistry II Laboratory (CHEM 3145, Dr. Shaun D. Black) Fall Semester 2023 Organic Chemistry II Laboratory Study Guide for Midterm Examination I What you should bring  A scientific calculator and a pencil with eraser  No note card is permitted What will be provided  A Periodic Table of the Elements  Relevant conversions/equations, but you should know basic equations and chemical reactions and/or structures  Scratch paper if you need it Hints  Review all pre-lab quizzes, videos, PowerPoint presentations, and your lab notebook  The questions on the exam will be reasonably straight forward, answerable with knowledge of organic chemistry and a little common sense  Just because it is not listed below does not mean that it might be asked on the exam!  Bolded items in the Key Concepts section below are of special importance  No practical will be included on this exam Safety Key Concepts  Focus on the highlights ( be prepared , goggles at all times, safety attitude , no food or drink, proper attire, etc .) and, then, specifics for each experiment  Review your safety sections in your laboratory notebook for any safety issues; know how to deal with each safety concern Accuracy and Precision  Understand accuracy and precision and how these are related to mean, standard deviation, and %Error  Be able to apply accuracy and precision to each experiment Quantitative Values and Their Measurement  Be sure to observe significant figures on all calculations  Be able to render numbers in scientific notation or convert scientific notation back to a rational number when appropriate  Remember all your SI multipliers ( milli -, micro -, nano -, pico -, femto -, etc .); use when appropriate  Understand dimensions and dimensional analysis  Apply basic statistics whenever appropriate ( e.g. mean, standard deviation, % errors)

E1: Separation and Analysis of “Panacetin”  Know the structures of aspirin (acetylsalicylic acid), Tylenol (acetaminophen), acetanilide , and phenacetin  Understand the concept of some drugs as pharmaceutical mixtures A pharmaceutical mixture is a mixture of active and non-active components used to treat a variety of things. Panacetin has a mixture of 10% sucrose, 40% acetylsalicylic acid (aspirin), and 50% of acetaminophen.  Understand the theory of this laboratory, as depicted in the following flow diagram:  Know the principles of polarity , like dissolves like , and extraction Polarity is the distribution of electrical charge over the atoms joined by the bond. Polar compounds dissolve polar compounds and nonpolar compounds dissolve nonpolar compounds. Extraction is the transference of compounds from a solid or liquid into a different solvent or phase. An example of this is using the separatory funnel to extract the organic layer on the bottom.  Why was sugar (sucrose) added to Panacetin ? It is an inactive ingredient used for the taste of the drug.  Why is trituration of your unknown with methylene chloride (CH 2 Cl 2 ) the most critical step of this procedure? The sucrose in the panacetin is not soluble in dichloromethane so it would separate the sucrose from the aspirin. The aspirin will dissolve and be liquid and the sucrose will remain a solid. This makes sure we separate the components of the unknown properly.

 Why was aqueous sodium bicarbonate used to extract aspirin? What would have happened if NaOH were used? What would have happened if HCl were used? Sodium bicarbonate was used to extract aspirin because it will deprotonate the carboxylic acid on acetyl salicylic acid (aspirin), moving it into the aqueous layer. If NaOH was used instead, it is a much stronger base so it would have done more than just deprotonate the carboxylic acid and completely messed up our products. If HCl was used, the separation of the aqueous layer in the separatory funnel would not fully work. This would cause aspirin to be left in the organic layer which would decrease the percent recovery of aspirin.  When you do an extraction, how many hands should be used to hold the separatory funnel ? What is the function of each hand? You should be using 2 hands to hold the separatory funnel. One hand should be holding the stopper in place in the funnel to make sure nothing spills out and the other hand should be opening the stopcock to vent the funnel frequently after each time you shake it up to relieve pressure.  When you vented your separatory funnel, what, chemically, was the gas released? Why is it important to vent your sep funnel into the hood? The gas released was carbon dioxide. It is important to vent the funnel into the hood so you don’t breath in large amounts of carbon dioxide.  Why do we do multiple small-volume extractions rather than one large extraction? Multiple extractions with small volumes are more efficient than one single extraction. Multiple small extractions will ensure that you are extracting more effectively.  Was the upper or lower layer of your extraction the organic phase in this experiment? The organic phase was the lower layer in the extraction because DCM is heavier and more dense than water as a halogenated solvent.  How could we tell which phase was which experimentally?  When we added HCl to the isolated aspirin, what chemical reaction took place? Why did acetylsalicylic acid precipitate from solution? Protonation took place and acetylsalicylic acid precipitated because it protonated the sodium salt we produced and reformed the acetylsalicylic acid.  Why was it better to use hand warmth to dry your unknown down as opposed to a hot plate? It was better to use hand warmth because a hot plate could evaporate out some of your final product.  How did you know that your unknown was dry? (identify two reasons)  What is good technique for a vacuum filtration ? (from set up to breaking the vacuum when you are done)  What does the % Recovery of each compound tell us?

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The percent recovery of each compound tells us how well we purified and separated the compounds. It tells us how pure our product is. It tells us how much of the compound is recovered after the reaction is complete. To calculate it is (experimental yield/theoretical yield)x100.  Understand how to calculate % Composition Percent composition is the mass of a component divided by the total mass of the mixture times 100.  What happened if your yield of aspirin and unknown were both low?  Understand the quantitative aspects of average melting range for an isolated compound. Why do we usually do 3 melting points per sample? What does the melting point tell us? If a compound is pure, what are the characteristics of the melting range? The melting point is reported with 2 numbers because the first one is when the compound starts melting and the second is when it is fully melted. The melting point range can tell us the identity of a compound and also how pure a compound is. We do an average of 3 because it further verifies that we have the correct melting point range. If a compound is pure, the melting point range, in theory, would be the same as the melting point of the compound itself from the sds sheet.  Identify the notable safety hazards of this experiment (identify two)

E2: Testing Markovnikov’s Rule  Know the essentials of Markovnikov’s Rule (nucleophile bonds to most substituted carbon of a double bond, or that the H bonds to the carbon of a double bond that contains the most hydrogens)  Understand the reaction and mechanism of Hydroboration-Oxidation (our procedure)

 Does hydroboration-oxidation lead to a Markovnikov or Anti-Markovnikov product ? Hydroboration-oxidation leads to antimarkovnikov product.  Understand each step of the procedure of this experiment  Why was reflux with an addition funnel useful during the hydroboration reaction?  Why was sodium borohydride (NaBH 4 ) used as the source of borane (BH 3 )? We used sodium borohydride and reacted it with iodine to make BH3 because it was more accessible.

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 Why was iodine added slowly to the hydroboration reaction?  Why is THF ( tetrahydrofuran ) a good solvent for this reaction? Because it stabilizes the borane.  Was 1-hexene the limiting reactant in this reaction? yes  What was the key reagent of the Oxidation phase of the reaction? H2O2  Why was potassium carbonate (K 2 CO 3 ) added during the final extraction?  What is the role of anhydrous MgSO 4 during the final work-up?  What was your % Recovery and how did it relate to the quality of your technique? Our percent recovery was 96%. That shows us that we created an almost completely pure 1- hexanol product. E3: Nuclear Magnetic Resonance Spectroscopy (NMR)  Understand 1 H- and 13 C-NMR and how to determine structures of molecules by NMR  Understand all functional groups (see handout in NMR 1 PowerPoint )  Review and re-master IR Spectroscopy; consider use of the “Divide-n-Conquer” method (see slide 5 in the NMR 1 PowerPoint )  Compare and contrast IR and NMR spectroscopies; what are the strengths and weaknesses of each?  Know the kind of information that can be gleaned from 1 H- and 13 C-NMR spectra  Describe the essential NMR experiment: nuclear (which nuclei?), magnetic (strong external magnet and nuclear magnetic dipole), resonance (the role of a 90 o pulse to reveal the Larmor precession of an NMR-active nucleus  Understand how precession is related to the Free Induction Decay (FID) obtained by the NMR spectrometer  Comprehend the role of the Fourier Transform on the production of an NMR spectrum from the FID  Identify common, useful NMR-active nuclei ( 1 H , 13 C , 15 N, 19 F, 31 P)  Understand the essential pieces of an NMR spectrometer  Know what “ upfield ” and “ downfield ” mean in an NMR spectrum, and that we label resonances a,b,c… going from upfield to downfield  Know the concept of electron shielding of nuclear magnetism and the relation to Chemical Shift  Understand why TMS (tetramethylsilane) is a good standard for 1 H-NMR

 Understand the  or ppm scale for the x-axis of an NMR spectrum; calculate ppm from the base resonance of a given spectrometer  Identify unique chemical environments for protons in a structure or on an NMR spectrum (remember to draw the structure with all hydrogens and in perspective if appropriate )  Describe the 0-2  upfield region of a 1 H-NMR spectrum as alkyl- ( sp 3 ) with the trend methyl- (-CH 3 ; ~0.9  ) , methylene- (-CH 2 -; ~1.2  ) , and methine- (-CH-; ~1.7  )  Understand the upfield to downfield trend for alkyne H < alkene H > aromatic H; understand the role of ring current  Know the approximate chemical shift placement of alkyl (0.5-2  ) , H near -=- or C=O (1.5- 2.5  ) , H near electronegative atom (N,O, F, Cl, Br) (2.5-4.5  ) , H on a double bond (4.5- 6.5  ) , aromatic H (6.5-8  ) , and H of an aldehyde or carboxylic acid (9-12  )  Understand the six major approaches in the solution of an 1 H-NMR spectrum: 1. DU (degrees of unsaturation, if possible; rings and/or unsaturations) 2. Number of signals (compare to empirical formula if available) 3. Chemical shift (moving from upfield resonances to downfield) a , b , c … 4. Integrals (number of hydrogens associated with each resonance) 5. J -coupling (splitting of signals), and (rarely) 6. Use of coupling constants (most useful for double bonds). Solve spectra in this order and by this strategy!  Describe the role of the “ N+1 Rule ” to assign splitting by adjacent hydrogens ( J -coupling )  Understand splitting into doublet , triplet , quartet , quintet, sextet, heptet, octet, nontet, and dectet and how these can be calculated from Pascal’s Triangle  Understand complex coupling that results from multiple nearby, different hydrogens  Understand complex splitting into multiplets ( e.g. doublet of doublets , doublet of triplets , etc. )  Identify strong coupling constants of cis (~7 Hz) or trans (~14 Hz) 1 H on alkenes  Understand the spectrometer-independent nature of the coupling constant  Describe unique properties of 1 H-NMR of alcohols (R-OH) and amines (R-NH)  Understand why cyclohexane has only one resonance  Understand the behavior of aromatic hydrogens (6.5-8  ) and splitting of these  Understand 13 C-NMR and the limited information that this can provide (# signals and chemical shift of C but not integrals or splitting and why these are not possible)  Know the general region for alkyl carbons (5-45  ) , C near N, O, F, Cl, Br (30-80  ) , C in triple bond (65-100  ), C in double bond (100-140  ), and carbonyl carbons (160-210  )  Do lots of practice problems of many kinds of compounds (see practice problem sets on Canvas with and without answers)  Remember that if your proposed structure is not consistent with all the information provided by an NMR spectrum, then your structure is wrong (partially or totally); i.e. the NMR spectrum accurately describes the energy of every proton or carbon in the molecule under consideration.

Useful equations Mean (average) 𝑥̅ = sum of results number of results = ∑ x i n ( x i are the individual measurements) Std deviation (SD) = s = √ sum of the squares of the deviations from the mean number of results - 1 = √ ∑( x i −𝑥̅) 2 𝑛−1 % error mean = |𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 − "𝑡𝑟𝑢𝑒" 𝑣𝑎𝑙𝑢𝑒| "true" value x 100% (related to accuracy) % error SD = 𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 𝑀𝑒𝑎𝑛 x 100% (measures precision,  2%) Mass % = mass of component total sample mass x 100% % recovery = mass of all dry components after separation initial dry mass x 100% % composition = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑜𝑛𝑒 𝑖𝑠𝑜𝑙𝑎𝑡𝑒𝑑 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑖𝑠𝑜𝑙𝑎𝑡𝑒𝑑 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠 x 100% Chemical shift =  = [𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑜𝑓 𝑛𝑢𝑐𝑙𝑒𝑢𝑠 (𝐻𝑧) − 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑜𝑓 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 (𝐻𝑧)] x 10 6 𝐵𝑎𝑠𝑒 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑜𝑓 𝑠𝑝𝑒𝑐𝑡𝑟𝑜𝑚𝑒𝑡𝑒𝑟 𝑖𝑛 𝑀𝐻𝑧

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