chem qn
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Hey. Some qns regarding tys mcq: 1) Is it right to assume that phenol does react with an acyl chloride to form an ester? I know that phenol is a weak nucleophile and it must be converted to a phenoxide ion. So the reaction btw phenol and acyl chloride proceeds at a slower rate than phenoxide ion and acyl chloride? 2)07/p1 qn 3 An excess of cold water was added to 0.3mol of a chloride in third period. 0.6molof hcl was formed. What was the chloride? Ans is pcl5.i thought pcl5 reacts in limited water to form pocl3 and 2hcl? Why cant the ans be mgcl2?
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Originally posted by pokepokee:
Hey. Some qns regarding tys mcq:
1) Is it right to assume that phenol does react with an acyl chloride to form an ester? I know that phenol is a weak nucleophile and it must be converted to a phenoxide ion. So the reaction btw phenol and acyl chloride proceeds at a slower rate than phenoxide ion and acyl chloride?
2)07/p1 qn 3 An excess of cold water was added to 0.3mol of a chloride in third period. 0.6molof hcl was formed. What was the chloride? Ans is pcl5.i thought pcl5 reacts in limited water to form pocl3 and 2hcl? Why cant the ans be mgcl2?Q1.
Acyl halides are indeed so feminine & chio (ie. electrophilic) that even guys (ie. nucleophiles) with weak balls (ie. not so electron-rich) are able to sexually (ie. chemically) react with. Deprotonating phenol to generate the stronger nucleophile phenoxide ion (ie. O atom with a -ve formal charge instead of merely a -ve partial charge) may in theory lower Ea and increase rate of reaction, but you've to be careful not to use excess NaOH (and it must be anhydrous!), else you'll be wasting your precious acyl halide chiobu that will be brutally ravaged away by your hired OH- ion mercenaries / soldiers / gangsters, as well as the horny water molecules if you had used aqueous NaOH.Q2.
The charge density of Mg2+ is not sufficiently high to generate 2x the moles of HCl. It only undergoes partial hydrolysis to generate a small fraction (relative to the moles of MgCl2) of HCl.Temperature is actually more important than limited/excess water. (Just as temperature is the more important factor when determining oxidation of alkenes to diols versus oxidative cleavage, over other factors such as pH and concentration).
Hence in cold water, 1 mole of PCl5 reacts with 1 mole of H2O to generate 1 mole of POCl3 and 2 moles of HCl.
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Ok. thanks :) 1) So concentrated naoh should be used to generate the phenoxide ion? 2) Can the explanation be used to explain why the ph of mgcl2 in water is 6.5 instead of 1? 3) I read cs toh's guide book and there is a phrase "__ more susceptible to electrophilic attack" I thought nucleophiles are the horny guys that will attck, not the electrophiles?
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Originally posted by pokepokee:
Ok. thanks
1) So concentrated naoh should be used to generate the phenoxide ion?
2) Can the explanation be used to explain why the ph of mgcl2 in water is 6.5 instead of 1?
3) I read cs toh’s guide book and there is a phrase ”__ more susceptible to electrophilic attack” I thought nucleophiles are the horny guys that will attck, not the electrophiles?
Q1. When reacting with acyl halides, phenol is sufficient. You only need to deprotonate phenol if you want to react with less feminine (electrophilic) species such as alkyl halides (aka halogenoalkanes).Q2. Yes. Al3+ is more acidic compared to Mg2+, because Al3+ has a significantly higher charge density, which means that it is more strongly electron-withdrawing by induction, and withdraws electron density more strongly from the water ligands, weakening the OH bonds of the water ligands, allowing protons to dissociate more readily (as the proton dissociation enthalpy becomes less endothermic).
Q3. In terms of mechanism, only nucleophiles (guys) have the balls to attack electrophiles (girls), 100% of the time, no exception (whether it is nucleophilic addition or electrophilic addition, it is still the nucleophile attacking the electrophile). The curved (or curly) arrows in a mechanism, illustrates the nucleophiles shooting out its balls (either a lone pair for OH- CN- Cl- nucleophiles, or pi bond for alkene and benzene nucleophiles) to form a new dative bond with the electrophile. In terms of wording, you can exercise a degree of flexibility and use both terms "nucleophilic attack" and "electrophilic attack", the latter term (as used by CS Toh) really meaning "reacting with the electrophile", or "the electrophile kena attack by".