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1-What is the difference between ESI-MS spectrum and CIDspectrum of leuenkephalin?a. Protonated ions are seen inESI-MS but not in CID spectrum. b. Doubly protonated...

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1-What is the difference between ESI-MS spectrum and CIDspectrum of leuenkephalin?a. Protonated ions are seen inESI-MS but not in CID spectrum. b. Doubly protonated ionsform. c. Fragmentation products of leuenkephalin isseen in ESI-MS but not in CIDspectrum. d. Fragmentation products ofleuenkephalin is seen in CID but not in ESI-MS. e.Protonatedions are seen in CID spectrum but not in ESI-MS spectrum2-According to the determination of N,N-dimethylaniline inpenicillin by GC, which of the follo

1-What is the difference between ESI-MS spectrum and CID spectrum of leuenkephalin?a. Protonated ions are seen in ESI-MS but not in CID spectrum. b. Doubly protonated ions form. c. Fragmentation products of leuenkephalin is seen in ESI-MS but not in CID spectrum. d. Fragmentation products of leuenkephalin is seen in CID but not in ESI-MS. e.Protonated ions are seen in CID spectrum but not in ESI-MS spectrum 2-According to the determination of N,N-dimethylaniline in penicillin by GC, which of the following is not correct? I. N, N-dimethylaniline is used during the purification of penicillin. II. N, N-dimethylaniline is an impurity in penicillin. III.N, N-dimethylaniline cannot be removed from penicillin IV. Maximum amount of N, N-dimethylaniline allowed is 20 ppm according to pharmacopoeia V.Naphthalene is used as an internal standard for the measurement of penicillin by GC. VI. Sample and standard solution of N, N dimethylaniline are analyzed and the peaks obtained are compared. VII. For the analysis of N, N-dimethylaniline in penicillin, N, N-dimethylaniline is dissolved in NaOH and extracted to cyclohexane. a. II, V, VI b. III, V, VII c. I, III, VII d. II, III, V e. III, IV, VII 3-in quantitation of penicillin by UV Vis spectroscopy, which one of the following is correct? I.Imidazole is a derivatization reagent. II.Penicillin does not have a chromophore. III.Penicillin derivatize has a maximum absorbance somewhere between 325 and 345 nm a. I and III b. Only II c. I, II and III d. I and II e. II and III 4-Which one of the following may act as interference in fluorescence emission spectroscopy? I. Heavy ions II.Complex formation III. UV absorbing species a. Only III b. II and III c. I, II and III d. I and III e. I and II 1-What is the difference between ESI-MS spectrum and CID spectrum of leuenkephalin?a. Protonated ions are seen in ESI-MS but not in CID spectrum. b. Doubly protonated ions form. c. Fragmentation products of leuenkephalin is seen in ESI-MS but not in CID spectrum. d. Fragmentation products of leuenkephalin is seen in CID but not in ESI-MS. e.Protonated ions are seen in CID spectrum but not in ESI-MS spectrum 2-According to the determination of N,N-dimethylaniline in penicillin by GC, which of the following is not correct? I. N, N-dimethylaniline is used during the purification of penicillin. II. N, N-dimethylaniline is an impurity in penicillin. III.N, N-dimethylaniline cannot be removed from penicillin IV. Maximum amount of N, N-dimethylaniline allowed is 20 ppm according to pharmacopoeia V.Naphthalene is used as an internal standard for the measurement of penicillin by GC. VI. Sample and standard solution of N, N dimethylaniline are analyzed and the peaks obtained are compared. VII. For the analysis of N, N-dimethylaniline in penicillin, N, N-dimethylaniline is dissolved in NaOH and extracted to cyclohexane. a. II, V, VI b. III, V, VII c. I, III, VII d. II, III, V e. III, IV, VII 3-in quantitation of penicillin by UV Vis spectroscopy, which one of the following is correct? I.Imidazole is a derivatization reagent. II.Penicillin does not have a chromophore. III.Penicillin derivatize has a maximum absorbance somewhere between 325 and 345 nm a. I and III b. Only II c. I, II and III d. I and II e. II and III 4-Which one of the following may act as interference in fluorescence emission spectroscopy? I. Heavy ions II.Complex formation III. UV absorbing species a. Only III b. II and III c. I, II and III d. I and III e. I and II



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THE SNAr MECHANISM: NUCLEOPHILIC AROMATIC SUBSTITUTION BY ADDITION-ELIMINATION Aromatic compounds bearing one or more strong electron-withdrawing substituents as well as a leaving group can sometimes undergo nucleophilic substitution instead of electrophilic substitution. The standard mechanisms of $\mathrm{S}_{\mathrm{N}} 2$ and $\mathrm{S}_{\mathrm{N}} 1$ reactions are not possible because of the $s p^{2}$ -hybridization at the carbons of a benzene ring, but a mechanism that involves nucleophilic addition followed by elimination, called $S_{\mathrm{N}} \mathrm{Ar}$ (nucleophilic aromatic substitution), is possible. For example chlorobenzene is not reactive toward $\mathrm{S}_{\mathrm{N}} 2$ or $\mathrm{S}_{\mathrm{N}} 1$ substitution by hydroxide. (FIGURE CANNOT COPY) However, if one or more strong electron-withdrawing groups is bonded ortho or para to the leaving group, substitution by a nucleophile is possible, as the following reactions show. (FIGURE CANNOT COPY) As the number of ortho and para electron-withdrawing groups increases, the temperature required for the reaction decreases, signifying an easier reaction. Meta groups do not produce a similar effect. $m$ -Chloronitrobenzene, for example, is unreactive. The mechanism that operates in these reactions is an addition-elimination mechanism involving the formation of a carbanion with delocalized clectrons, called a Meisenheimer intermediate. The process is called nucleophilic aromatic substitution $\left(\mathrm{S}_{\mathrm{N}} \mathrm{Ar}\right) .$ In the first step of the following example, addition of a hydroxide ion to $p$ -nitrochlorobenzene produces the carbanion; then elimination of a chloride ion yields the substitution product as the aromaticity of the ring is recovered. (FIGURE CANNOT COPY) Carbanion (Meisenheimer intermediate) Structures of the contributing resonance forms are shown further below. The carbanion is stabilized by electron-withdrawing groups in the positions ortho and para to the halogen atom. If we examine the following resonance structures for a Meisenheimer intermediate, we can see how: (FIGURE CANNOT COPY) Especially stable (Negative charges are both on oxygen atoms.) What is the product of the following reaction? (FIGURE CANNOT COPY) STRATEGY AND ANSWER: NaH is a strong base that will convert 4 -methylphenol to its phenoxide salt. $1-(p-$ Toluenesulfonyl)-2,6-dinitrobenzene contains both a good leaving group and two strong electron-withdrawing groups. Thus the likely reaction is a nucleophilic aromatic substitution $\left(S_{N} A r\right),$ leading to the following diaryl ether. 1-Fluoro-2,4-dinitrobenzene is highly reactive toward nucleophilic substitution through an S_yAr mechanism. (In Section 24.5 B we shall see how this reagent is used in the Sanger method for determining the structures of proteins.) What product would be formed when 1-fluoro-2,4-dinitrobenzene reacts with each of the following reagents? (a) EtONa (b) $\mathrm{NH}_{3}$ (c) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}$ (d) EtSNa THE CHEMISTRY OF... Bacterial Dehalogenation of a PCB Derivative Polychlorinated biphenyls (PCBs) are compounds that were once used in a variety of electrical devices, industrial applications, and polymers. Their use and production were banned in $1979,$ however, owing to the toxicity of PCBs and their tendency to accumulate in the food chain. 4-Chlorobenzoic acidis adegradation product of some PCBs. It is now known that certain bacteria are able to dehalogenate 4-chlorobenzoic acid by an enzymatic nucleophilic aromatic substitution reaction. The product is 4-hydroxybenzoic acid, and a mechanism for this enzyme-catalyzed process is shown here. The sequence begins with the thioester of 4-chlorobenzoic acid derived from coenzyme A (CoA): (FIGURE CANNOT COPY) Some key features of this enzymatic SyAr mechanism are the following. The nucleophile that attacks the chlorinated benzene ring is a carboxylate anion of the enzyme. When the carboxylate attacks, positively charged groups within the enzyme stabilize the additional electron density that develops in the thioester carbonyl group of the Meisenheimer intermediate. Collapse of the Meisenheimer intermediate, with rearomatization of the ring and loss of the chloride ion, results in an intermediate where the substrate is covalently bonded to the enzyme as an ester. Hydrolysis of this ester linkage involves a water molecule whose nucleophilicity has been enhanced by a basic site within the enzyme. Hydrolysis of the ester releases 4-hydroxybenzoic acid and leaves the enzyme ready to catalyze another reaction cycle.

Predict products or the fallen reactions. Dorian L. Sulfuric. That's Ah. So finish which goes toe the pair in the positions because 63 group is a hearted contributed a dollar dessert. Is it liberation? The car parks. A group is a resonance except her. Yeah, the try substitution goes to the net position Bremen nation off matter benzene. The letter group is an inductive, except er and business, except er so substitution goes to the net position insulation or for isopropyl Benzia I support group. That's ah Harper conjugated donor. So substitution goes toe the parrot in Ortho position. However you to the stereo hinderance imposed by the I support group. The author I, Samir is almost not existent. Just traces its most repaired. I, Samir.

Fennel visited, which can be produced from funeral, is less reactive than funeral in automatic. There are a few exceptions fearful. Explain what it's this, but the group is still Order Pereira director. Just like hydroxy group, you know, So I don't see a group in. Fino is a force of credit director because over too long in the pants, which supplies elections, most it through the orphan and better positions, this group still has to look natural in prayer on oxygen, which pretty X the same way as the age group. In funeral, however, the compound is less reactive because for conjugation off long and compare with adjusting Gruber. No, which most away park the church former our since one So the little there compares on oxygen become less active.

Using it isn't serious and b r plus, as an example on a profile. Explain why the hydroxy group in Funeral is actuator and Fourth of Prayer. Oxygen in the first group restroom won't compare, and they can be donated to Vedrine by the residents donated effect, which in creatures that been seen in with electoral and make it more susceptible toe therapeutic substitution. They and it over foreign affairs off oxygen because off its electro negativity that's inducted, defect cannot contract the stronger residence defect. And this The net effect is even stronger in the Sigma products, which is intermediate in the traffic automatic substitution. So it's an activator. No, let's write free Christmas tortures over its cinema complex when benzene with B R plus. So there was the charge is Jellicle ized Dream two orphan and one pair position. With respect to Borman. No, let's place for H in the fourth position and see if it's a good or the director or which group is next through the crab. With the price of charge, there's a excellent opportunity to forced organization by the business donating effect. So which group is an official order for director? No, let's please the ritual in the middle position. Now you can see that in my the reason structures or each group is attached to the carbon with a partial positive charge. So the actuated defect or for age, so the middle position is much weaker. A little still activation. But it's Rica than actuacion through the or the position. No, let's drive a planner or hate your job. The pair of age group. Now it's again attached carbon with a partial positive charge. So documentation is begin very official, because off the residence, the nation off the long compare on oxygen so the age group is also in a better direction.

Predict results for the two foreign reaction. One finger prep. In with its shell, it's you will return it while a figure prepping and bread use a more stable Ben Zizek crocodile ritual. Capture CR minus on Give the world the alternative. Kavika Tile at this carbon would be less stable because of the leg off education with it benzene for hundreds inoculation. The reaction proceeds through Make uranium on the press. The charge will be distributed between America and roaster gerbils, and this carbon will have more positive charge because it will be better. Gillick allies back in education with the benzene. So this position, well being attacked with water with the bunt with maker comes off on America is a benched through the other carbon and then deport the nation and removal, or for America by reducing agent Junior it in Alcohol River Bridge Group in the bin Zigic position


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