Ochem II lab midterm extended

Learn about how different leaving groups on the ring can affect the Nucleophilic Aromatic Substitution reaction.

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Learn about the impact of substituents on the ring during the Nucleophilic Aromatic Substitution reaction (both electron-withdrawing and electron-donating group).

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What is the major organic product obtained from the following reaction? 1 2 3 4

3

How many reducing equivalents are present in each unit of sodium borohydride, NaBH4NaBH4 1 2 3 4

4

How the structure of diene and dienophile can affect the rate of Diels-Alder reaction.

???

What is carbocation? How many different types of carbocations are possible? How can the stability of carbocation affect the rate of an SN-1 reaction?

A carbocation is a carbon molecule that has a positive charge and lacks electrons (hybridizion and substituents do not matter). 4 types of carbo cations are possible. (look at image) In an SN1 reaction, the rate determining step is the loss of the leaving group to form the intermediate carbocation. The more stable the carbocation is, the easier it is to form, and the faster the SN1 reaction will be.

Which task must be carried out before using a round-bottom flask at the lab bench? Select one: · Hot flasks must be allowed to cool to room temperature. · A stir plate should be set up and plugged in. · A large area of the bench must be cleared in case the flask begins to roll. · A proper support, such as a cork ring, should be set in place.

A proper support, such as a cork ring, should be set in place.

Identify items that can be used to control the boiling when heating liquid in a round bottom flask. Select one or more: · A stir bar and stir plate · A Bunsen burner · A rubber stopper or cork · Boiling chips or stones

A stir bar and stir plate Boiling chips or stones

When drying an organic solution, how is it determined that enough drying agent has been added? All drying agent in the flask will become a powder. · All drying agent in the flask will clump up. · All drying agent in the flask will dissolve. · Any newly-added drying agent remains a powder, instead of clumping up.

Any newly-added drying agent remains a powder, instead of clumping up.

When working in a fume hood, what is the best position of the hood sash? Select one: · At eye level · As high as possible, to the top of the hood · Completely closed · As low as possible, no more than halfway up

As low as possible, no more than halfway up

What are the reasons to determine the melting point of a sample in a melting point apparatus? Select one or more: · Assessment of the sample's purity · Identification of an unknown sample · Removal of impurities from the sample

Assessment of the sample's purity Identification of an unknown sample

Which feature represents a carbonyl group? Select one: C=OC=O · C−ClC−Cl · O−HO−H · C−O

C=OC=O

Identify the characteristics of a good recrystallization solvent. Select one or more: · Dissolves a sample well at low temperatures. · Does not dissolve a sample well at high temperatures. · Does not dissolve a sample well at low temperatures. · Is not an organic liquid with a low boiling point. · Dissolves a sample well at high temperatures.

Does not dissolve a sample well at low temperatures. Dissolves a sample well at high temperatures

5. Which of these structures is a conjugated diene? a. I and III b. I, III, V c. II and IV d. II, IV, V e. All of these structures are conjugated dienes

II and IV

Why are we using NaBH4 instead of LiAlH4 in the experiment?

LAH reduces more aggressively than NBH. Water and aqueous alcohol can be used as solvents in its reactions. NaBH4, which has a lower reactivity toward water, is preferred as a reagent for reducing aldehyde or ketone. NBH also is easier to use as it reacts with probic solvents slowly at room temperature and can be used with alcohols as the solvent.

'Maleic anhydride is considered as good dienophile'- Why?

Maleic anhydride is also a very good dienophile, because the electron-withdrawing effect of the carbonyl groups causes the two alkene carbons to be electron-poor, and thus a good target for attack by the pi electrons in the diene.

What do you mean by "protic" and aprotic" solvents? Give two examples in each case.

Protic solvents have O-H and N-H bonds and they can form hydrogen bonds. Aprotic solvents may have hydrogen atoms on them somewhere, but they are not directly attached to O or N (lack O-H or N-H bonds) and therefore cannot do hydrogen bonding.

What is Markovnikov's rule? Be able to use it to predict the major/minor products if given an electrophilic addition reaction.

RICH GET RICHER!!!! NEVER TRUST CAPITALISM. jk When you add a hydrogen halide (HX) to an unsymmetrical alkene, the hydrogen (proton) gets added to the LESS substituted carbon (carbon with more hydrogens) while the halogen gets added to the MORE substituted carbon thus leading to the formation of the most stable carbocation intermediate.

Which type of alkyl halide can give the best yield?

The Williamson synthesis gives the best yields with primary alkyl halides Why? because the more there is attached to our halogen, the more competition there is for bonding leading to a lower yield. (don't forget the best leaving groups!!! : I > Br > Cl > F)

What is the purpose of using base (methoxide ion) in this reaction?

To deprotonate the alcohol. methoxide acts as the base removing the proton from the acidic phenol group, depronating the alcohol.

What is the name for the anionic intermediate formed during a nucleophilic aromatic substitution reaction?

Wheland intermediate or a sigma complex (Miesenhiemer complex??)

Between NaBH4 and LiAlH4, which one is a stronger reducing agent? Why?

When comparing NaBH4 with LiAlH4, the metal-hydrogen bond of LiAlH4 is more polar; thus, it is a stronger reducing agent than NaBH4. This is mainly because aluminum in LiAlH4 is more electronegative than boron in NaBH4. lithium aluminum hydride can reduce acids, esters, amides, aldehydes, and ketones. sodium borohydride will only reduce ketones and aldehydes at room temp.

When should you replace your gloves in an organic lab? Select one or more: · When the gloves have been exposed to a solvent · When you handle a new piece of glassware · When you mix two chemicals in the lab · When there is any visible tear in the gloves

When there is any visible tear in the gloves When the gloves have been exposed to a solvent

Xylene is considered as an excellent solvent for Diels-Alder reactions', why?

Xylene (dimethylbenzene) is used as a high-boiling point solvent so that the reaction will work fast enough to complete conveniently. Xylene also has a low freezing point, making the experiment possible in cold conditions.

ANOTHER MEME BREAK

YOUVE GOT THIS!!! KEEP GRINDING DEB HAS NOTHING ON YOU

How would you make a benzene ring susceptible to nucleophilic attack?

You want to make the benzene ring negatively charged

meme break

Youre doing great. Keep up the hard work!

2. Identify the conjugated diene from the following options. A. 4-methyl-1,3-heptadiene B. 3-methyl-1,5-heptadiene C. 2-methyl-2,5-heptadiene D. 4-methyl-1,4-heptadiene E. 5-methyl-2,3-heptadiene

a

Identify the one which is the perfect example for Isolated double bond? a) 1,4 pentadiene b) 1,2 pentadiene c) 1,3 pentadiene d) 1,5 butadiene

a) 1,4 pentadiene

What are the characteristics of a nucleophile for a substitution reaction?

an alkoxide ion is a nucleophile that dispenses a halide ion from an alkyl halide to give an ether

Which of these molecules could not be made using a Diels-Alderreaction? a b c d

b

The reactant shown below can follow which type of reaction mechanism a) Williamson ether synthesis b) Diels Elder Reaction c) Markovnikov addition d) Anti-markovnikov addition

b) Diels Elder Reaction

Conjugated diene reacts with which among the following to form a cyclohexene? a) Phenol b) Dienophile c) Hexane d) Tribromo phenol

b) Dienophile

A molecule in which more than one single bond separates two double bonds are called as ____________ a) Coordinate bond b) Isolated double bond c) Cumulative double bond d) Conjugated double bond

b) Isolated double bond

Why is sodium borohydride an important reagent in reducing a ketone? a) It is good for hydrolysis type reactions b) It is a good source of the hydride ion (H-) c) It can act as a base d) It can act as a free radical initiator.

b) It is a good source of the hydride ion (H-)

Which class of compound is an example of a carbonyl compound? a) alcohol b) carboxylic acid c) alkene d) alkane

b) carboxylic acid

What is meant by the term bumping?

bumping is the sudden uncontrolled boiling of the liquid. its commonly observed when boiling organic liquids that have a relatively low boiling points.

3. What is the correct classification of the following pericyclic reaction? A. electrophilic addition B. sigmatropic rearrangement C. cycloaddition D. electrocyclic reaction E. nucleophilic substitution

c

Which is unreactive in hydride reduction with NaBH4? a b c d

c

Identify the statement which is related to Diels-Alder reaction? a) It is very stereospecific b) Molecular distortion takes place c) Cyclic dienes react very slow than the linear chain dienes d) Addition of maleic anhydride to cyclopentadiene causes diene and dienophile to produce different products

c) Cyclic dienes react very slow than the linear chain dienes

1. Dienes precisely separated by one σ bond are classified as ______. A. isolated B. cumulated C. skipped D. conjugated E. terminal

d

Which pairing of diene and dienophile would lead to the product shown? a b c d

d

Which of the following functional groups is indicated by a strong and broad infrared absorption around 3300 cm-1? a. Carbonyl b. Alkene c. Alkane d. Alcohol e. Amined.

d. Alcohol

If both the carbonyl groups in benzil are reduced by NaBH4, which will be the final product?

hydrobenzoin

What type of alcohol formation will be favored by the hydration of an alkene primary secondary teritiary

secondary

What are the common reducing agents which can be used to reduce a carbonyl group?

sodium borohydride NaBH4) and lithium aluminum hydride (LiAlH4)

Predict the stability of carbocation.

tertiary > secondary > primary > methyl

What do you mean by an "opposite-side" attack in substitution reaction?

the nucleophile attacks the electrophilc center on the side that is opposite to the leaving group

What is a heteroatom in an organic compound? Select one: · The central C atom in the carbon chain. · The C atom at the end of the longest chain · Any atom other than C or H · Any Group 17 element such as chlorine, fluorine, or bromine

· Any atom other than C or H ·