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Orgo Lab > FINAL FINAL FINAL EXAM > Flashcards

FINAL FINAL FINAL EXAM Flashcards

1
Q

How do you calculate the mole ratio of your product:contaminant?

A
  1. Pick a signal from the product molecule and divide integration number by the number of H atoms represented by that peak.
  2. Do the same for the contaminant/impurity.
  3. Compare these two numbers in a ratio.
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2
Q

How do you calculate a mass ratio of product: contaminant?

A
  1. Multiply the mole ratio by respective product and contaminant molecular weights
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3
Q

How do you calculate mass% of product in your sample with a contaminant?

A
  1. divide (mass of product) / (combined mass of product and contaminant)
  2. Multiply by 100%
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4
Q

How do you calculate theoretical yield of a reaction?

A
  1. If there is more than one reactant, determine the limiting reactant:
    a. convert grams of reactant(s) to moles of reactant(s)
    b convert moles of reactant(s) to moles of product using the chemical equation’s mole ratio
    c. the reactant that produces the lowest mole amount is the limiting reagent
  2. With the limiting reagent mass, calculate grams of product produced (this is theoretical yield
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5
Q

How do you calculate the percent yield of a reaction?

A
  1. Divide experimental yield (given) by the theoretical yield (calculated)
  2. Multiply by 100%
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6
Q

How do you calculate the index of hydrogen deficiency?

A

= (2C + 2 - H)/2
- add 1 to numerator for every N/P
- subtract 1 to numerator for every halogen
- ignore Oxygen/Sulfur

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7
Q

What does Beilstein Test test for?

A

Presence of Halogen

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8
Q

What does Benedict’s Test test for?

A

Presence of reducing carbohydrates/hemiacetals.

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9
Q

What does the Bicarbonate Test test for?

A

Presence of Carboxylic Acids and Sulfonic Acids

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10
Q

What does the Bromine Test test for?

A

Unsaturation (not aromatics)

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11
Q

What does the Jones Test test for?

A

Aldehydes
primary alcohols
secondary alcohols

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12
Q

What does the 2,4-DNPH/Brady’s Test test for?

A

Aldehydes and Ketones

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13
Q

What does the Ferric Hydroxamate Test test for?

A

Esters

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14
Q

What does the Iodoform Test test for?

A

Methyl Ketones
secondary alcohols next to a methyl group

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15
Q

What does the Lucas Test test for?

A

Tertiary alcohols
Secondary alcohols

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16
Q

What does the Permanganate/Baeyer Test test for?

A

Unsaturation

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17
Q

What does the pH Test test for?

A

Carboxylic and Sulfonic Acids

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18
Q

What does the Phenol Test test for?

A

phenols

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19
Q

What does the silver nitrate Test test for?

A

Tertiary alkyl halides
Secondary alkyl halides

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20
Q

What does the Sodium Iodide/Finkelstein Test test for?

A

Primary and secondary alkyl chlorides and bromides

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21
Q

What does the Tollens Test test for?

A

Aldehydes

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22
Q

What does the Semicarbazone Test test for?

A

Aldehydes and Ketones

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23
Q

What is the mechanism of the Jones test?

A
  • Reagent: CrO3 in H2SO4
  • Positive Result: Orange Cr6+ reagent becomes blue-green Cr3+ and precipitates
  • Negative Result: Orange Cr6+ remains Cr6+
  • Positive-Testing Compounds: Aldehydes, primary alcohols, secondary alcohols
  • Chemical Reaction: aldehydes and primary alcohols become carboxylic acids // secondary alcohols become ketones
24
Q

What is the mechanism of the Tollens test?

A
  • Reagent: Ag(NH3)2+
  • Positive Result: Elemental silver mirror/black precipitate = Ag(s) forms
  • Negative Result: No precipitate
  • Positive-Testing Compounds: Aldehyde
  • Chemical Reaction: Aldehyde becomes carboxylic acid
25
Q

What is the mechanism of the Lucas Test?

A
  • Reagent: HCl and ZnCl2
  • Positive Result: Cloudiness due to precipitate
  • Negative Result: Clear and no precipitate
  • Positive-Testing Compounds: Secondary and Tertiary alcohols (secondary is slower than tertiary)
  • Chemical Reaction: Chlorine substitution where OH was
26
Q

What is the mechanism of the Phenol/FeCl3 test?

A
  • Reagent: FeCl3
  • Positive Result: Dark blue, purple, or red
  • Negative Result: no color change/ stays yellow (color of Fe3+)
  • Positive-Testing Compounds: phenols
  • Chemical Reaction: formation of Fe3+ complex with phenols, attached through the Oxygen
27
Q

What is the mechanism of the Baeyer test?

A
  • Reagent: KMnO4
  • Positive Result: Deep purple reagent (KMnO4 - potassium permanganate) reduced to brown precipitate (MnO2 - manganese dioxide)
  • Negative Result: No color change / stays deep purple color / no precipitate
  • Positive-Testing Compounds: Unsaturation, Aldehydes
  • Chemical Reaction: Alkene becomes doubly substituted alcohol / Aldehyde becomes carboxylic acid
28
Q

What is the mechanism of the Iodoform Test?

A
  • Reagent: Iodine (I2) and Iodide (I-) in NaOH
  • Positive Result: Canary yellow precipitate and cloudiness due to CHI3 production
  • Negative Result: no color change / stays light yellow or orange
  • Positive-Testing Compounds: Secondary alcohols adjacent to methyl and methyl ketones
  • Chemical Reaction: Secondary alcohol and ketone become carboxylate anion and CHI3
29
Q

What is the mechanism of the semicarbazone test?

A
  • Reagent: Semicarbazide hydrochloride (**know structure)
  • Positive Result: White precipitate and changed melting point of product
  • Negative Result: No precipitate / unchanged melting point
  • Positive-Testing Compounds: Ketones and Aldehydes
  • Chemical Reaction: both aldehydes and ketones become attached to the (formerly Cl-substituted) Nitrogen in semicarbazide via the C=O bond changing to C=N
30
Q

What is the mechanism of the 2,4-DNPH Test?

A
  • reagent: 2,4-dinitrophenylhydrazine (***know structure)
  • Positive Result: color change from transparent orange to red, orange, yellow precipitate
  • Negative Result: No color change from transparent orange and no precipitate
  • Positive-Testing Compounds: Aldehydes and Ketones
  • Chemical Reaction: Both aldehydes and ketones become attached to the (formerly NH2) Nitrogen in dinitrophenylhydrazine via the C=O bond changing to C=N
31
Q

What is the mechanism of the Bromine Test?

A
  • Reagent: Bromine in Water
  • Positive Result: Decolorization of reagent, clear
  • Negative Result: Stays orange
  • Positive-Testing Compounds: Alkenes, unsaturation
  • Chemical Reaction: C=C double bonds (non-aromatics) become substituted with Bromine
32
Q

What methods could be used to test for the number of C=C bonds present?

A
  • 1H NMR would give the number of sp2-hybridized Carbons and their non-equivalency
  • UV absorbance would also differentiate the C=C bonds
33
Q
  1. Why do we not perform a simple distillation on lemongrass oil at atmospheric pressure to separate the components?
  2. What’s the advantage of steam distillation?
  3. What is another distillation method that might work?
A
  1. Simple distillation would subject the reactive compounds to temperatures that might decompose the compounds
  2. Steam distillation avoids this by limiting the temperatures to 100C
  3. Vacuum distillation would be the better alternative, since it can be done at room temperature or lower
34
Q

What are the structures of Carvone, Cuminaldehyde, Eugenol, and Citral? How can they be differentiated?

A
  1. Carvone: unsaturation and no aldehyde
  2. Cuminaldehyde: saturated and aldehyde
  3. Eugenol: unsaturation and no aldehyde
  4. Citral: unsaturated and aldehyde

Use Bromine and Tollens test to differentiate the four compounds (not carvone and eugenol)

35
Q
  1. What would taking an IR of an unknown tell you about its structure?
A

An IR should distinguish between an alcohol, and aldehyde or a ketone by virtue of the uniqueness of the OH, C(=O)-H and C=O absorptions.

36
Q

Which kind of mechanism can better account for the product mixture obtained from the dehydration of cis and trans 2-methyl cyclohexanol: E1, E2 or a combination of the two?

A

A combination of the mechanisms makes the most sense because the cis-isomer gives the expected, more substituted product, while the trans-isomer gives a nearly even mixture, and even some of rearrangement product (via hydride shift)

37
Q

Describe and explain the possible effect on your results of the following experimental errors:
a. you forgot to add the phosphoric acid
b. you used a simple distillation apparatus instead of a fractional distillations set up with a Vigreaux column
c. The 2-methylcyclohexanol you used was actually the pure trans-isomer rather than a mixture of isomers

A

a. The reaction won’t proceed at all
b. The separation of the primary product might be more difficult, and you will get more B in A
c. You will get a higher % of Product B, relative to a 50:50 cis-trans starting mixture

38
Q

In the background section, 1-methylcyclohexene and 3-methylcyclohexene were mentioned as possible products of the dehydration of 2-methylcyclohexanol.

Why was 2-methylcyclohexene not mentioned as a possible product of the dehydration of 2-methylcyclohexanol?

A

Nomenclature/isomer, methyl group on the double bond is assigned position 1

39
Q

If the density of methylenecyclohexane is 0.80 and the bp = 102-103C, do you think you would be able to readily separate it by distillation from the other products of the dehydration?

A

It is possible, but it would require very careful fractional distillation using a high performance distillation column.
The density might make it easier to separate, because it is lighter than the other products.

40
Q

You wish to substituted bromine in the following molecules with a nucleophile, explain whether the given molecule would react by the Sn2 or Sn2 mechanisms and explain why:
a. 1-methyl-1bromocyclohexane
b. 1-bromopropane
c. 2-bromohexane

A

a. SN1 because there is steric hindrance around the carbon reaction center, leaving no hydrogens available for the SN2 mechanism // the formation of a stable carbocation is favored in this situation
b. SN2 because it is less sterically hindered and there is little resistance to nucleophilic approach // energy of primary carbocations is so high that they have a lower tendency to form an intermediate, making an SN1 reaction very unlikely
c. SN1 or Sn2, secondary alkyl halides have moderate steric hindrance that allows for both mechanisms to occur // nature of solvent would determine which mechanism would be favored in this situation

41
Q

Why does benzyl bromide react under both SN1 conditions and SN2 conditions?

A

Benzyl bromide acts as a primary alkyl halide, and it shows Sn2 substitution. However, benzyl bromide can also form a stable carbocation when a bromide ion is lost. The benzyl cation is resonance stabilized. Hence Benzyl bromide can show both Sn1 as well as Sn2 pathways.

42
Q

Why is bromobenzene nonreactive under both SN1 and SN2 conditions?

A

Bromobenzene contains no hydrogens around the reacting center and the conjugated system of the benzene ring allows no transfer of energy, making both mechanisms virtually impossible

43
Q

If bromocyclohexane reacts faster than chlorocyclohexane in an SN2 reaction, what could be the reason?

A

Bromine is a better leaving group than chlorine. This is due to the fact that Br-Carbon bonds are weaker than Cl-Carbon bonds, making it easier for Br-Carbon bonds to be broken and for the Br group to be kicked off. In addition, bromine is a less basic anion and is less electronegative than chlorine, both factors contributing to its better leaving ability.

44
Q

Tertiary-butyl iodide reacts faster that t-butyl bormide via SN1 mechanism because iodide is a better leaving group than bromide. Why?

A

Iodine-Carbon bonds are the weakest, making Iodide a better leaving group than any other halide. The relative low strength of the iodine-carbon bonds is due to iodine’s lower electronegativity than the other halides. Iodine has a lower attraction for electrons and protons than the other halides. In addition, iodide is the least basic among the halide anions, and the least basic is the best leaving group.

45
Q

To promote the SN1 mechanism, we used AgNO3 in a polar, protic solvent. Why?

A

A polar solvent stabilizes the charge-separated transition state and lowers the activation energy. Therefore, polar solvent increases the reaction rate for SN1 mechanisms. A polar solvent that is also protic further stabilizes the transition state because as the leaving group becomes negatively charged, hydrogen bonding develops.

46
Q

Why was acid used to quench the Grignard reaction?

A

Acid will protonate the oxyanion from the addition of the anion to the ketone. It will also assist in destroying excess Grignard, and also react with any undissolved Mg turnings

47
Q

Why does methyl benzoate, which is water insoluble, dissolve in concentration H2SO4?

A

The sulfuric acid protonates the carbonyl oxygen, creating an ionic species which then dissolves sufficiently in the acid for the reaction to proceed. This is why we are careful with the ratio of sulfuric acid to ester and keep it cool so that ester hydrolysis does not occur to any great extent.

48
Q

In the nitration of methyl benzoate, which undesired products may have formed which would have lowered the yield? What procedural error may have led to these products?

A
  • In order or probability: dinitro, para, ortho
  • failure to control the temperature when mixing the sulfuric acid and when adding the nitric-sulfuric acid mixture can cause these
  • not controlling the temperature after the acid mixture is added to the ester/acid combination
  • These problems are more likely when the quantities of reactants are significantly greater than those we use (why scale was reduced for this reaction)
49
Q

In the nitration procedure, several washes with cold methanol were done. Why was it important to use cold methanol?

A

The product is very soluble in room temperature methanol, so its critical that the wash methanol be cold to remove the acids and starting material selectively

50
Q

Why was it important to use a minimum amount of methanol for recrystallization?

A

The product is highly soluble in MeOH, so one uses as little as possible so it can be precipitate simply using cooling

51
Q

What species removes the hydrogen from the sp3 carbon in the cationic reaction intermediate to allow the aromatic ring to form? (Nitration of Methyl Benzoate)

A

Water

52
Q

What will be the primary difference(s) in the 1H NMR of salicylic acid and aspirin?

A

Salicylic acid will have a phenol peak
Aspirin will have a CH3 peak

53
Q

In the recrystallization step, why should you not add boiling H2O to the ethanol solution?

A
54
Q

What qualitative test would you use to determine if any of salicylic acid remained in your product?

A

FeCl3 test / Phenol test

55
Q

How would you solubilize the aspirin for a FeCl3 test?

A

Since aspirin is not very soluble in water, you would use methylene chloride to dissolve the compound before adding FeCl3

56
Q

Why does NaCl help to precipitate the soap from aqueous solutions?

A

NaCl donates Na+ ions that shift equilibrium toward the formation of soap. (Le Chatelier’s Principle)

57
Q

Why do sodium acetate and sodium propionate make poor soaps?

A

Their hydrocarbon tails are too short to attach to and remove nonpolar substances like grease and oil.

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