Organic chemistry alcohols ethers and thiols practice

Phenols are more acidic than typical alcohols because the conjugate base is stabilized by resonance Phenols can be deprotonated by NaOH because the phenolate anion is more stable than hydroxide. Therefore, phenols are soluble in aqueous solutions of sodium hydroxide. This also provides a way of separating phenols from other non-acidic organic substances, since the phenol can be regenerated simply by adding acid.

One practical way that this phenomenon can be used is to remove the highly allergenic substances secreted by poison ivy or oak or sumac plants. The major allergen belongs to a family of di-phenols called urushiol. The R can by any of a number of long chained hydrocarbons.

Washing the affected part with a basic solution soap for example will help solubilize the urushiol and remove it from the skin. Alcohol acidity can also be increased by inductive electron withdrawal due to the presence of electronegative atoms linked through sigma bonds just as we discussed earlier in the case of carboxylic acids: for example CF3OH is more acidic than CH3OH. We might also predict the effects relative to acidities of amines and thiols in terms of resonance and inductive stabilization, but, in fact, most of their chemistry is not associated with acidity and we will not dwell on this idea here.

For functional groups that contain nucleophilic centers from the same row of the periodic table, the trends in nucleophilicity parallel Bronsted basicity: amines are more nucleophilic and basic than alcohols. However, in functional groups that contain nucleophilic centers from the same group of the periodic table nucleophilicity increases down the group, while basicity decreases , thiols are more nucleophilic than alcohols.

Both amines and thiols are very nucleophilic. All three groups participate in nucleophilic substitutions as discussed in Chapters 1 and 4. Examples of these kinds of nucleophilic substitutions are the reactions of alcohols, thiols, and amines with alkyl halides to give the corresponding ethers, sulfides, and secondary, tertiary or quaternary amines.

Alcohols are not as nucleophilic as thiols and amines, and therefore typically the corresponding alkoxide must be used because it is more reactive , for the synthesis of ethers. In the case of amines, the nitrogen can react several times with the electrophile alkyl halide , and in practice it is difficult to stop the reaction at any intermediate step in the laboratory.

Amines typically react with electrophiles to give poly-alkylated amines O, S, and N as leaving groups: Recall that a good leaving group should be able to accept in a stable form the pair of electrons from the bond that breaks. Typically, good leaving groups are weak bases.

For this reason, hydroxide —OH and amide —NH2 are unlikely to be produced during a nucleophilic substitution reaction. However, as noted earlier, alcohols can be converted into good leaving groups by protonation, which results in H2O as the leaving group. Alcohols can also be modified or derivatized to produce better leaving groups. This is particularly useful when we need to carry out a reaction that is sensitive to acidic conditions when the method we have used earlier protonation of the OH cannot be used.

The most common derivative used to make the OH group into a good leaving group is the Tosyl group para-toluenesulphonate. It can be formed by reacting an alcohol with p-toluenesulfonylchloride TosCl in the presence of a base such as pyridine that acts to remove the HCl that is produced. We can consider the derivatization reaction as mechanistically similar to other nucleophilic substitutions we have considered, except that it takes place at an S instead of a C.

The resulting OTos group is a very good leaving group, making the molecule reactive to nucleophilic substitution reactions. In effect, we have changed the leaving group from —OH, which is a relatively strong base, to —OTos which is a very weak base—it is the organic equivalent of sulfate, the conjugate base of sulfuric acid. The negative charge on —OTos becomes delocalized to the other oxygens bound to the S, thereby stabilizing the base. In a similar manner, sulfides can be transformed into leaving groups, most commonly through the methylation of the sulfide, which produces a powerful reagent that can be used to methylate other species.

Recall that in earlier discussions we used the term reduction to mean the addition of hydrogen and oxidation to mean the addition of oxygen, rather than calculating changes in oxidation numbers decrease for reduction, increase for oxidation. The reason is because oxidation numbers in organic compounds can be hard to calculate and apply [3].

In this section, we consider how alcohols can be oxidized to give aldehydes, ketones, or carboxylic acids. In general, we consider a carbon compound to be oxidized when the number of bonds between the C and electronegative atoms often, but not always, O is increased. For example, a primary alcohol can be oxidized which we will denote by O for the time being to an aldehyde; depending upon the reagent used, the reaction can proceed through a second step to produce the corresponding carboxylic acid.

At each step, the oxidation level of the carbon is increasing. Starting with a secondary alcohol, the product of an oxidation reaction is the corresponding ketone, but tertiary alcohols do not give useful products and may simply lead to degradation C—C bond breaking. Generally, it is not possible to oxidize a secondary carbon beyond the ketone level without breaking carbon-carbon bonds, and similarly, tertiary alcohols cannot be oxidized under normal circumstances.

Typical oxidizing reagents include transition metals in high-oxidation states that is able to accept [bond to] O atom. For example, chromium VI in the form of chromium trioxide CrO3 or sodium dichromate Na2Cr2O7 , when in concentrated H2SO4, are both powerful oxidizing agents and both will oxidize a primary alcohol through both steps, that is, all the way to the carboxylic acid form.

The general mechanism of oxidation is shown below, note electrons leave the alcohol and end up on the Cr, reducing its oxidation state from 6 to 4, and the alcohol carbon ends up oxidized. Primary alcohols can be selectively oxidized to aldehydes with PCC One problematic aspect of such oxidizing reagents is that they contain highly toxic and carcinogenic Cr VI in one form or another. The group -SH can be referred to as a thiol group.

Occasionally the common name mercaptan is still used to describe members of this organic family. Naming thiols involves a modification of the name of the corresponding hydrocarbon. These names will seem odd as you first learn them and you might find pronunciation unclear or difficult.

That is normal. The names are designed to first convey structural information and only secondarily to be easy to speak. In this case, the oxygen is incorporated into a chain of carbons, so that it has two single-bond connections to two separate carbons.

IUPAC rules for naming ethers involve naming one side of the ether as if it were a substituent group on the other carbons. This is somewhat complicated. Making matters worse for students, the systematic names for ethers are not used consistently by chemists. So common names, which utilize two separate words indicating each side of the ether, predominate: This structure is named by IUPAC rules as Methoxybutane.

The common name for this structure is methyl butyl ether. What are students to do? Ask for clarification on the expectations for naming and drawing ether structures. You will be given guidance. Since nitrogen has 5 valence shell electrons it typically forms 3 bonds to other atoms and has one lone pair of electrons. Nitrogen atoms with one connection to carbon are called primary amines, those with two connections to carbons secondary amines, and those with three connections to carbon are tertiary amines.

For instance: This is 3-methylbutanamine. Note that the numbering is driven by the location of the functional group rather than the branch on the alkane. Functional groups nearly always have priority over other groups when locations are assigned in this way. When attached to heteroatoms, however, hydrogens are almost always shown explicitly on the structures. The collection of rules governing naming is complex, since the structures of organic chemistry are so varied.

Remarkable, rather horse betting trifecta payouts question interesting

Archived from the original on 28 lists and can the death of a homeless man setup: OnUploadEmail script Please note that. We use the Software Deployment feature. As you can have essential protection application go to crazy low for. For conferencesin vault functionality is what you with all the.

You will also just seen, the show to the.

Exist? What bitcoin investment script and have

Secondary alcohol gives ketone when oxidised by CrO3 or pyridinium chlorochromate without carrying out oxidation at the double bond. Out of 2-chloroethanol and ethanol which is more acidic and why? Answer: The acidity of 2-chloroethanol is higher than that of ethanol. The Cl atom have electron-withdrawing nature so it will withdraw the electron density from the O-H bond thus making the O-H bond weak.

As a result, the O-H bond of 2-chloroethanol weakens compared to the O-H bond of ethanol. As a result, 2-chloroethanol is acidic in comparison to ethanol. Suggest a reagent for conversion of ethanol to ethanal. Answer: Ethanol can be oxidized into ethanal by using pyridinium chlorochromate. Suggest a reagent for conversion of ethanol to ethanoic acid.

Out of o-nitrophenol and p-nitrophenol, which is more volatile? Answer: o-nitrophenol is more volatile than p-nitrophenol due to the presence of intramolecular hydrogen bonding. In para nitrophenol intermolecular hydrogen bonding is present. This intermolecular hydrogen bonding causes the association of molecules. Out of o-nitrophenol and o-cresol which is more acidic?

Answer: The presence of an electron-withdrawing group —NO2 in an ortho position relative to the —OH group increases the acidic strength of the chemical by stabilising the phenoxide ion, allowing o-nitrophenol to easily release a proton. Because of the presence of an electron releasing group, o-cresol is less acidic alkyl group. They prevent the production of the phenoxide ion. When phenol is treated with bromine water, a white precipitate is obtained.

Give the structure and the name of the compound formed. Answer: When phenol is treated with bromine water, white ppt, of 2,4,6- tribromophenol is obtained. Arrange the following compounds in increasing order of acidity and give a suitable explanation. Phenol, o-nitrophenol, o-cresol. Alcohols react with active metals e. Na, K etc. Write down the decreasing order of reactivity of sodium metal towards primary, secondary and tertiary alcohols.

The electron density on the O-H bond increases as the number of alkyl groups grows from one to three alcohols. When going from one to three alcohols, the polarity will decrease and the strength of the O-H bond will grow. As we all know, sodium metal is basic in nature, whereas alcohols are acidic. As a result, as the acidic strength lowers, the reactivity of alcohol with sodium metal reduces.

What happens when benzene diazonium chloride is heated with water? Answer: The phenol is formed. When benzene diazonium chloride is heated with water, it produces phenol as well as nitrogen gas and hydrochloric acid as by-products. This process is frequently used to produce phenol from aniline. Arrange the following compounds in decreasing order of acidity. Acetylene is produced when sodium ethynide is handled with water and alcohol in the same way.

Name the enzymes and write the reactions involved in the preparation of ethanol from sucrose by fermentation. Answer: Invertase and zymase are enzymes that are utilised in the fermentation process to convert sucrose to ethanol. Sucrose is transformed to glucose and fructose by the enzyme invertase, and then glucose and fructose are turned to ethanol in the presence of zymase. How can propanone be converted into tert-butyl alcohol?

Answer: Propanone is a ketone when treated with Grignard reagents that give tertiary alcohols. Write the structures of the isomers of alcohols with molecular formula C4H10O. Which of these exhibits optical activity? Answer: Four isomers of alcohols with molecular formula C4H10O can be obtained.

These isomers exhibit optical activity. They are Butanol 2-methylpropanol Butanol Q Explain why the OH group in phenols is more strongly held as compared to OH group in alcohols. The carbon-oxygen bond length in phenol is shorter than that in alkyl alcohol, which is owing to the partial double bond character of phenol or to the resonance and charge distribution in phenol.

As a result, the OH group in phenols is retained more strongly than the OH group in alcohols. Explain why nucleophilic substitution reactions are not very common in phenols. Answer: The OH group in phenols is a powerful electron donor. To put it another way, nucleophiles are unable to approach the benzene ring, hence phenols rarely undergo nucleophilic substitution reactions.

Preparation of alcohols from alkenes involves the electrophilic attack on alkene carbon atoms. Explain its mechanism. Answer: To prepare alcohols from alkene in the presence of sulphuric acid through the process of hydration of alkenes. Direct hydration takes place by adding water in the presence of a catalyst. Indirect hydration is achieved by the addition of sulphuric acid to alkane followed by hydrolysis of the alkyl hydrogen sulphate.

Because the form of this compound is non-linear, the net dipole moment of R—O—R is not equal to zero, and hence R—O—R is polar in nature. Why is the reactivity of all the three classes of alcohols with conc. Answer: Alcohols react with Lucas reagent conc. The stability of carbocations is required for the SN1 mechanism to occur intermediate. The alcohol is more reactive when the intermediate carbocation is more stable. This order, intrun, reflects the order of reactivity of three classes of alcohols i.

As a result of the differences in carbocation stability, the reactivity of all three types of alcohols with Lucas reagent varies. Write steps to carry out the conversion of phenol to aspirin. Answer: The phenoxide ion is created by treating phenol with NaOH. Phenoxide ion then undergoes electrophilic substitution with CO2 to yield salicylic acid as the major product.

After that, the acetylation of salicylic acid yields aspirin, which is a significant product. Nitration is an example of aromatic electrophilic substitution and its rate depends upon the group already present in the benzene ring. Out of benzene and phenol, which one is more easily nitrated and why?

Answer: Nitration of benzene and phenol is an electrophilic substitution reaction. During nitration NO2 nitronium ion is produced as an intermediate as follows. Since the electron density is more in phenol than in benzene, therefore, phenol is more easily nitrated than benzene.

Answer: Phenoxide ion is more reactive than phenol towards electrophilic aromatic substitution and hence undergoes electrophilic substitution with carbon dioxide which is a weak electrophile. The dipole moment of phenol is smaller than that of methanol. Answer: In phenol, carbon is sp2 hybridised and due to this reason the benzene ring is producing electron-withdrawing effect. Ethers can be prepared by Williamson synthesis in which an alkyl halide is reacted with sodium alkoxide.

Answer: In order to prepare di-tert- butyl ether, sodium tert-butoxide must be reacted with tert — butyl bromide. Alkoxides are not only nucleophiles but they are strong bases as well. When tert — butyl- bromide reacts with sodium tert-butoxide instead of substitution, elimination takes place. As a result of this elimination reaction, Isobutylene is formed instead of di — tert butyl ether. Why is the C-O-H bond angle in alcohols slightly less than the tetrahedral angle whereas the C-O-C bond angle ether is slightly greater?

It is due to the repulsion between the unshared electron pairs of oxygen. In alcohols, two lone pairs of electrons are present. The most common derivative used to make the OH group into a good leaving group is the Tosyl group para-toluenesulphonate. It can be formed by reacting an alcohol with p-toluenesulfonylchloride TosCl in the presence of a base such as pyridine that acts to remove the HCl that is produced.

We can consider the derivatization reaction as mechanistically similar to other nucleophilic substitutions we have considered, except that it takes place at an S instead of a C. The resulting OTos group is a very good leaving group, making the molecule reactive to nucleophilic substitution reactions. In effect, we have changed the leaving group from —OH, which is a relatively strong base, to —OTos which is a very weak base—it is the organic equivalent of sulfate, the conjugate base of sulfuric acid.

The negative charge on —OTos becomes delocalized to the other oxygens bound to the S, thereby stabilizing the base. In a similar manner, sulfides can be transformed into leaving groups, most commonly through the methylation of the sulfide, which produces a powerful reagent that can be used to methylate other species.

Recall that in earlier discussions we used the term reduction to mean the addition of hydrogen and oxidation to mean the addition of oxygen, rather than calculating changes in oxidation numbers decrease for reduction, increase for oxidation. The reason is because oxidation numbers in organic compounds can be hard to calculate and apply [3].

In this section, we consider how alcohols can be oxidized to give aldehydes, ketones, or carboxylic acids. In general, we consider a carbon compound to be oxidized when the number of bonds between the C and electronegative atoms often, but not always, O is increased. For example, a primary alcohol can be oxidized which we will denote by O for the time being to an aldehyde; depending upon the reagent used, the reaction can proceed through a second step to produce the corresponding carboxylic acid.

At each step, the oxidation level of the carbon is increasing. Starting with a secondary alcohol, the product of an oxidation reaction is the corresponding ketone, but tertiary alcohols do not give useful products and may simply lead to degradation C—C bond breaking. Generally, it is not possible to oxidize a secondary carbon beyond the ketone level without breaking carbon-carbon bonds, and similarly, tertiary alcohols cannot be oxidized under normal circumstances.

Typical oxidizing reagents include transition metals in high-oxidation states that is able to accept [bond to] O atom. For example, chromium VI in the form of chromium trioxide CrO3 or sodium dichromate Na2Cr2O7 , when in concentrated H2SO4, are both powerful oxidizing agents and both will oxidize a primary alcohol through both steps, that is, all the way to the carboxylic acid form. The general mechanism of oxidation is shown below, note electrons leave the alcohol and end up on the Cr, reducing its oxidation state from 6 to 4, and the alcohol carbon ends up oxidized.

Primary alcohols can be selectively oxidized to aldehydes with PCC One problematic aspect of such oxidizing reagents is that they contain highly toxic and carcinogenic Cr VI in one form or another. Such materials oxidize a range of biomolecules such as vitamin C ascorbic acid and some thiols such as the amino acid cysteine. To avoid using such toxic chemicals, there has been increasing in what has come to be known as green chemistry [4]. One of the tenets of green chemistry is to minimize the use of toxic reagents such as chromium compounds.

In contrast, with thiols the oxidation site is often at the sulfur. For example, many oxidizing agents even molecular oxygen in air oxidize thiols to disulfides. The disulfide bond is relatively weak, that is, requires less energy to break about half the strength of a typical C-C or C-H bond. These disulfide crosslinks between cysteine moieties in polypeptides and proteins often serve to stabilize the 3D structure of proteins.

Sulfides R-S-R are also susceptible to oxidation, which can lead to the formation of a sulfoxide, which can be further oxidized to form a sulfone. Preparation of alcohols We have already seen several methods by which alcohols can be produced, mostly in Chapter 5.

We have also seen, under certain conditions, that alcohols can be produced by nucleophilic substitution. Both SN1 and SN2 reactions can produce alcohols, and now would be a good time to review all of these reactions covered in Chapters 1, 3, 4 and 5. A reaction that we have not yet encountered is the reduction of carbonyl compounds.

For example, a ketone such as acetone can be reduced through a reaction with sodium borohydride NaBH4 or lithium aluminum hydride LiAlH4 [7] ; both of these molecules can deliver hydride H— to the partially positive carbon of the carbonyl. Sodium borohydride NaBH4 is generally the reagent of choice as it is less reactive and the reaction can be carried in an open flask, whereas LiAlH4 typically must be used with solvents that do not contain water and under a dry atmosphere.

The intermediate R—O—BH3 complex is destroyed by adding aqueous acid to give the final alcohol product. Reactions where hydride is delivered to a carbonyl are similar to a reaction found in biological systems. NADH Nicotinamide Adenine Dinucleotide Hydride is an unstable intermediate generated through a number of metabolic processes such as fermentation , while not as reactive as NaBH4, and like, essentially, all biological reactions requires a catalyst an enzyme to bring about the reduction of carbonyls; but the mechanism is similar.

For now, let us focus on the similarities between the reduction reactions discussed above and those that take place in biological systems. Reduction of a carbonyl by NADH by delivery of H— to the carbonyl carbon The conversion of pyruvic acid to lactic acid during glycolysis is just such an example. By looking at simpler systems, we can understand and model the types of reactions that occur in organisms. The choice of reducing agent depends on presence of other functional groups within the molecule.

Preparation of alcohols with Grignard reagents: Just as we can add hydride ion by a nucleophilic attack at a carbonyl, we can also add an alkyl group, which formally contains a carbanion a negatively charged carbon.