How can I tell if a halogenated hydrocarbon and sodium alk are being eliminated or nucleophilic subs

Chemical propertiesHalogenated hydrocarbons are an important class of organic synthesis intermediates, which are the starting materials for many organic synthesis, and it can undergo many chemical reactions, such as substitution reactions, elimination reactions, etc. The halogens in alkyl halides are easily replaced by many nucleophiles (nu) such as Oh, Or, CN, NH3 or H2NR to generate corresponding alcohols, ethers, nitriles, amines and other compounds, and the general reaction formula can be written as: r x :

nu─→r─nu＋:x

Iodine is the most prone to substitution reaction, followed by bromoalkane, chlorinated alkane, and aryl and vinyl halides are difficult to have similar reactions due to the strong connection of carbon halide bonds.

Halogenated hydrocarbons can undergo a elimination reaction, and the hydrogen halide is removed under the action of an alkaline alcohol solution to form carbon-carbon double bonds or carbon-carbon triple bonds

For example, ethyl bromide undergoes a dissolution reaction in the alcohol solution of sodium hydroxide to produce ethylene gas, sodium bromide and water.

In addition to the reaction of dehalogenation, o-dihalogen compounds can also undergo dehalogenation reaction to form olefins under the action of zinc powder (or nickel powder). In addition, some halogenated hydrocarbons, under the action of strong bases, are able to undergo -elimination, resulting in carbene. For example, chloroform reacts with potassium tert-butanol to produce dichlorocarbene, etc.:

Halogenated hydrocarbons. Halogenated hydrocarbons can react with certain metals to form organometallic compounds, such as reaction with lithium, magnesium, etc., to form organolithium and organomagnesium compounds, which are extremely important reagents in organic synthesis, among which magnesium reagents are called Gria reagents.

Summary. The nucleophilic substitution of alcohols mainly carries out the substitution reaction according to the SN2 mechanism: the hydrolysis reaction occurs by halogenated hydrocarbons and NaOH H2O, and the reaction of SN1 or SN2 is determined according to the different halogenated hydrocarbons.

Addition reaction: the raw material is generally olefin, according to the different reaction reagents, the site of the hydroxyl group is also different, such as borohydration-oxidation reaction, the hydroxyl group is on the carbon that is less replaced, and in the hydroxymercury reaction, the hydroxyl group is on the carbon that replaces more, and the addition of simple and water under acidic conditions depends on the carbocation stability and is likely to rearrange.

Reduction reaction: Alcohol is obtained by the reaction of aldehydes, ketones, acids, esters and reducing agents, such as LAH, NaBH4, RED-AL, etc.

What are the similarities and differences between the nucleophilic substitution of halogenated hydrocarbons and the nucleophilic substitution of alcohols?

The nucleophilic substitution of alcohols mainly carries out the substitution reaction according to the SN2 mechanism: the hydrolysis reaction occurs by halogenated hydrocarbons and NaOH H2O, and the reaction of SN1 or SN2 is determined according to the different halogenated hydrocarbons. Addition reaction:

For example, in the borohydration-oxidation reaction, the hydroxyl group is on the carbon that is less replaced, while in the hydroxymergylation reaction, the hydroxyl group is on the carbon that is substituted more, and the addition of simple and water under acidic conditions depends on the carbocation stability and is likely to rearrange. Reduction reaction: alcohol is obtained by the reaction of aldehydes, ketones, acids, esters and reducing agents, such as lah, NabH4, red-al, etc.

Hood skillful. Halogenated hydrocarbons are much more reactive than hydrocarbons and can undergo a variety of chemical reactions that can be converted into various other types of compounds.

1.The reaction mechanism is different: SN1 is a single-molecule nucleophilic substitution reaction, and the alkyl halide first forms a planar carbocation and then reacts with a nucleophile. SN2 is a bimolecular nucleophilic substitution reaction, and the reagent attack on the substrate to form a new bond is synchronized with the cleavage of the degrouping group, and the three-dimensional configuration of the substrate undergoes a Walden transformation (configuration reversal) in this Yenianchen process.

The nucleophilic substitution reactions of halogenated hydrocarbons are as follows:

Reaction mechanism of SN1 with SN2A, SN2 (Bimolecular Nucleophlic Substitution) Ho + CH3 BR.

Difference Between Electrophilic Addition and Nucleophilic Bonus:

First, the substance is different:

Substances that are electronegative are called nucleophiles. For example, RmgX where the MgX part is electropositive and R(alkyl) is negative, which is a nucleophilic test disorder agent, and the addition to the carbonyl group is a nucleophilic addition reaction. Because the carbon of the carbonyl group is electropositive.

The nucleophilic reaction is that the halogens of common halogenated hydrocarbons are replaced by nucleophiles such as Ho—, Ro—, Cl—, Br—, CN—, R3N—, H2O, and RoH.

Second, the meaning is different:

The most common electrophilic substitution is the Friedel-Crafts alkylation reaction that occurs in the benzene ring. where R attacks the benzene ring as a positive ion (Rx is an electrophile). Electrophilic additions mostly occur in the addition of HCl, HBR (electrophiles) and alkenes and alkynes.

The H cation first attacks the double bond with high electron density (electrophilic addition), and the Cl anion attacks the carbocation.

Need to know: The most representative reaction is the reaction of the carbonyl group of aldehydes or ketones with the addition of Grignard reagent. Rehydrolyzed to obtain alcohol, which is a good way to synthesize alcohol.

In the carbonyl group, o is slightly electronegative; In Grignard reagent, C-Mg is linked, Mg is slightly electropositive, and C is the nucleophilic site. The nucleophilic carbon of the format reagent then attacks the electrophilic carbonyl carbon, the double bond opens, and a new C-C bond is formed.

Water, alcohols, amines, and substances containing cyanide ions can all be added to carbonyls. The nucleophilic addition of the triple bond of carbon and nitrogen (cyano) is mainly manifested by hydrolysis to form a carboxyl group. In addition, the carbon-carbon triple bond of terminal alkyne can also undergo nucleophilic addition with nucleophiles such as HCN, such as acetylene and hydrocyanic acid to form acrylonitrile (CH2=CH-CN).

Sodium iodide (Nai) usually reacts with halogenated hydrocarbons according to the nucleophilic substitution reaction mechanism.

Nucleophilic substitution reaction is a common organic chemical reaction in which a nucleophile, such as sodium iodide, attacks a halogen atom in a halogenated hydrocarbon molecule, displacing it and forming a new chemical bond. In the case of sodium iodide, its main role is to provide iodine ions (I-), which is a nucleophile that attacks halogenated hydrocarbon molecules.

In terms of ascending precursors, sodium iodide can undergo nucleophilic substitution reactions with halogenated hydrocarbons, in which iodide ions (i-) attack halogen atoms (e.g., chlorine, bromine) in the halogenated hydrocarbon molecule and replace them. The result of the reaction is the production of the corresponding iodinated hydrocarbons and sodium salts.

Nucleophilic substitution reactions typically follow the SN2 (nucleophilic substitution two) mechanism, which means that the reaction takes place in a single step with the simultaneous participation of nucleophiles and halogenated hydrocarbons, and the rate of the reaction depends on the concentration of both. However, in some cases, the SN1 (nucleophilic substitution one) mechanism may also occur, in which case the reaction is divided into two steps, first forming an electrophilic hydrocarbon intermediate followed by nucleophilic substitution. However, for the reaction of sodium iodide and halogenated hydrocarbons, the SN2 mechanism is generally more common.

The main reason why halogenated hydrocarbons generally do not have substitution reactions with sodium hydroxide is that sodium hydroxide is a basic substance, and the halogen atoms (such as chlorine, bromine, etc.) in halogenated hydrocarbons are weak electrophilic groups. Under alkaline conditions, sodium hydroxide will form hydroxide ions (OH-), which have strong electrophilicity and are more likely to react with halogenated hydrocarbons with weak electrophilicity. As a result, halogenated hydrocarbons are more likely to undergo elimination reactions rather than substitution reactions under alkaline conditions.

The elimination reaction is when the halogen atoms and hydroxide ions (OH-) in the halogenated hydrocarbons combine with each other to form halogen ions and water molecules, and at the same time release another molecule (such as HCl, HBR, etc.). This reaction results in a decrease in the halogen atoms on the hydrocarbon group instead of being replaced by other groups. Hand ants.

In conclusion, halogenated hydrocarbons are more likely to undergo elimination reactions rather than substitution reactions under alkaline conditions, which is due to the influence of the electrophilic properties of various ions in the reaction and the electrophilic properties of halogen atoms.

Halogenated hydrocarbons (halogenated hydrocarbons refer to organic compounds containing halogen atoms in the molecule) are not easy to substitute with sodium hydroxide in some cases, which is mainly related to the reaction mechanism and chemical properties.

Under alkaline conditions, sodium hydroxide (NaOH) provides hydroxide ions (OH-), which leads to a substitution reaction. However, the reactivity of halogenated hydrocarbons usually depends on the type of halogen (fluorine, chlorine, bromine or iodine) and its molecular structure. Here are some reasons why halogenated hydrocarbons are not prone to substitution reaction with sodium hydroxide in some cases:

Size of halogen atoms: The size of halogen atoms increases gradually, from fluorine to iodine, and the atomic radius increases. Due to the larger iodine atom, the iodogenated hydrocarbons have weaker carbon-halogen bonds and lower reactivity, so iodinated hydrocarbons are not easy to substitute with sodium hydroxide.

Polarity of carbon-halogen bonds: The carbon-halogen bonds of halogenated hydrocarbons are usually polar and halogen atoms are electronegative due to the lower electronegativity of carbon atoms. In some cases, the reactivity of halogenated hydrocarbons may be reduced due to the polar nature of the carbon-halogen bond, making them less prone to substitution reactions with sodium hydroxide.

Effect of Groups: Other groups in the molecular structure of halogenated hydrocarbons may also affect the reactivity. Certain groups may hinder the substitution reaction from proceeding, resulting in a reaction that is less likely to occur.

Although halogenated hydrocarbons are not easily substituted with hydrogen for sodium oxide, they can still occur under certain conditions. To achieve specific reaction results, factors such as the molecular structure of halogenated hydrocarbons, reaction conditions, and possible side reactions need to be considered.

Both alcohols and halogenated hydrocarbons can undergo nucleophilic substitution reactions and elimination reactions, and the activity of halogenated hydrocarbons is much higher.

Halide ions are better than hydroxide ions as the leaving group, and the nucleophilic substitution reaction of halides can be smoothly reacted at a lower temperature, such as our commonly used Friedel-Crafts reaction, etherification reaction. On the contrary, the departure of hydroxide ions is much more difficult, and even if the protonated hydroxyl group leaves, it is not so easy, and it often requires harsh conditions such as concentrated sulfuric acid.

Because the nucleophilic substitution reaction and elimination reaction of alcohol produce water, which is much more environmentally friendly than halogenated hydrocarbons as raw materials, it is of great significance to study the nucleophilic substitution reaction and elimination reaction of alcohol replacing halogenated hydrocarbons in the process of green synthetic chemistry, once the technological breakthrough is made.

First, the acidity and alkalinity are different:

1. Alcohol needs an acidic environment.

2. Halogenated hydrocarbons need an alkaline environment.

Second, the reaction mechanism is different:

1. The mechanism of alcohol reaction is that the hydroxyl group first combines with a hydrogen ion, thus forming a positively charged hydroxyl group + group, this group takes an electron and leaves in the form of water, and then the H on the adjacent C will leave in the form of hydrogen ions to ensure the conservation of charge.

2. The elimination of halogenated hydrocarbons is to attack C adjacent to the halogen atom first, and remove the H above, which requires an alkaline environment, and the halogen atom gets an electron to leave in the form of ions.

The acidity and alkalinity of the conditions under which alcohols and halogenated hydrocarbons are eliminated are different.

The mechanism of the alcohol reaction is that the hydroxyl group first combines with a hydrogen ion, thus forming a positively charged - Oh2+ group, this group takes an electron and leaves in the form of water, and then the H on the adjacent C will leave in the form of H+ to ensure the conservation of charge, so the alcohol elimination reaction is carried out under acidic conditions. The elimination of halogenated hydrocarbons is to first attack C adjacent to the halogen atom C, and remove the H above, this step requires an alkaline environment, and then the halogen atom gets an electron and leaves in the form of ions.

Therefore, the difference between the two elimination reaction conditions is the difference in acidity and alkalinity. Alcohols require an acidic environment, whereas halogenated hydrocarbons require an alkaline environment.