Identify the acidity and alkalinity of organic matter, and how to compare the acidity of organic mat

The acidity can be judged by comparing the stability of the negative ions.

The electron cloud density and spatial effect of the central atom were analyzed to determine the alkalinity.

The acidity and alkalinity of organic compounds can be used to separate compounds in organic chemistry and compare differences in the reactivity of substances.

The answer is supplemented. 1. Acidity and alkalinity can be determined by analyzing electronic effects (induction effect, conjugation effect).

The induction effect affects the acidity and alkalinity of a substance: the greater the ability of a substance to give protons, the more acidic it is. And the ability to give protons depends largely on the ability of the substituents around the molecule to lose protons to form negative ions to disperse the charge.

The more dispersed the charge of the formed carboxanion is, the stronger and more stable the ability to donate protons. Therefore, any structural factor that disperses the charge can increase the stability of the carboanion and decrease the stability of the negative ion. In general, electron-withdrawing substituents increase the acidity of organic matter, while electron-donating substituents reduce their acidity.

The conjugation effect also affects acidity and alkalinity. In a conjugated system, electron delocalization expands the range of electron motion and makes the system stable. The carbonyl group in a carbonyl compound is a polar double bond, which makes its -hydrogen somewhat acidic due to the induction effect and the conjugation effect.

However, the acidity of hydrogen varies depending on the chemical environment.

2. For organic compounds with different structures, the acidity and alkalinity of the chemical compounds can be compared through some reactions.

Some chemical substances have large differences in their structure, and it is difficult to determine the relationship between their acidity and alkalinity through the spatial effect of electronic effects, such as: sodium acetylene, sodium amino, sodium hydroxide, these three compounds are all alkalis, and the order of their alkalinity is not known at a glance, but it can be compared by the relevant reactions existing in the literature, and the acidity and alkalinity of organic Taiwan substances can be seen at a glance

HC=CH+NANH2-11HC= CNA+H3

HC==CNA+HO——一HC==CH+Naoh

It is not difficult to see from the above that according to the rule that weak alkali and weak acid react to weak acid and weak alkali, the alkalinity of sodium aminogen is stronger than that of sodium acetylene, and the alkalinity of sodium acetylene is stronger than that of sodium hydroxide, on the other hand, it also shows that acetylene is more acidic than ammonia, and acetylene is weaker acidic than water After knowing this, it is not difficult for us to understand that the reaction involving sodium acetylene and some other carboanion ions often must be carried out under anhydrous conditions It is also an effective means to determine the acid-alkaline relationship between chemical substances through some reactions

In short, to judge the acidity and alkalinity of organic compounds, we can consider the following aspects: for organic compounds with similar structures, their acidity and alkalinity can be compared by electronic effects (including induction effect and conjugation effect); For organic compounds with different structures, their acidity and alkalinity should be judged according to the relevant reactions in the literature.

Hydroxide ions are alkaline.

With sulfate ions, nitrate ions, carbonate ions, and phosphate ions are all acidic.

Of course, there are some substances whose acidity and alkalinity cannot be seen from the chemical formula.

No, some organic substances with the same chemical formula are not different substances of the same structure.

Basic Principles for Comparing the Acidity of Organic Matter:

The shorter the hydrocarbon group, the stronger the acidity at the same element.

Because methyl group is an electron-pushing group, due to its action, the oxygen-hydrogen electron pair in the carboxyl group will be biased towards hydrogen and the polarity will be weakened.

As the number of carbon atoms increases, the electron pushing effect weakens, and the polarity of the oxygen-hydrogen bond increases, making it easier for h to detach from oxygen. ）

The carboxyl group is also more acidic when it is attached to the benzene ring;

The more carboxyl groups, the more acidic they are.

In middle school, it is common to memorize the mantra of weak acidity (the acidity gradually decreases from front to back, and only the comparison of the first level of ionization is considered).

Thiophosphate hydrofluoric acid, nitrosformic acid, glacial acetic acid, bicarbonate hydrocyanilic acid.

Other common acids such as HCO4, H2SO4, HNO3, Hi, and HBR are all strong acids, and strong acids are considered to be acidic equivalents in water (the leveling effect of water makes the strong acids completely ionized in the first stage).