Read More
Date: 18-5-2017
![]()
Date: 7-7-2019
![]()
Date: 16-8-2019
![]() |
Terminal alkynes are much more acidic than most other hydrocarbons. Removal of the proton leads to the formation of an acetylide anion, RC=C:-. The origin of the enhanced acidity can be attributed to the stability of the acetylide anion, which has the unpaired electrons in an sp hybridized orbital. The stability results from occupying an orbital with a high degree of s-orbital character. There is a strong correlation between s-character in the orbital containing the non-bonding electrons in the anion and the acidity of hydrocarbons. The enhanced acidity with greater s-character occurs despite the fact that the homolytic C-H BDE is larger.
Compound | Conjugate Base | Hybridization | "s Character" | pKa | C-H BDE (kJ/mol) |
---|---|---|---|---|---|
CH3CH3 | CH3CH2- | sp3 | 25% | 50 | 410 |
CH2CH2 | CH2CH- | sp2 | 33% | 44 | 473 |
HCCH | HCC- | sp | 50% | 25 | 523 |
Consequently, acetylide anions can be readily formed by deprotonation using a sufficiently strong base. Amide anion (NH2-), in the form of NaNH2 is commonly used for the formation of acetylide anions.
|
|
دراسة: عدم ترتيب الغرفة قد يدل على مشاكل نفسية
|
|
|
|
|
علماء: تغير المناخ تسبب في ارتفاع الحرارة خلال موسم الحج
|
|
|
|
|
جهود مكثفة وطباعة عشرات الآلاف من المنشورات .. استعدادات العتبة العلوية المقدسة لعيد الغدير الأغر
|
|
|