Direct (or 1,2) addition means that the nucleophile attacks the carbonyl group directly. An addition compound is formed which may lose X−, if it is a leaving group, or become protonated to give an alcohol.

Conjugate (or 1,4) addition means that the nucleophile adds to the end of the alkene furthest from the carbonyl group. The electrons move through into the carbonyl group to produce an enolate anion that usually becomes protonated to give a ketone.

The fi rst difference between the two routes is that the product from direct addition keeps the alkene but loses the carbonyl group while conjugate addition keeps the carbonyl group but loses the alkene. As a C=O π bond is stronger than a C=C π bond, conjugate addition gives the thermodynamic product. But as the carbonyl group is more electrophilic than the far end of the alkene, especially to charged, hard nucleophiles, direct addition gives the kinetic product. So direct addition is favoured by low temperatures and short reaction times while conjugate addition is favoured by higher temperatures and longer reaction times, provided the 1,2 addition is reversible.

The second difference depends on how electrophilic is the α,β-unsaturated carbonyl com pound. The more electrophilic such as aldehydes and acid chlorides tend to prefer direct addition while the less electrophilic such as ketones or esters tend to prefer conjugate addition.

It is similar with the choice of nucleophile: more nucleophilic species, such as MeLi or Grignard reagents, prefer direct addition, particularly as they react irreversibly, while less nucleophilic species like amines and thiols prefer conjugate addition. These nucleophiles add reversibly to the C=O group, giving an opportunity for any direct addition product to revert to starting materials and react again.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الدينية يُطلق دورة فقهية دينية لملاكات مستشفى الكفيل

شعبة فاطمة بنت أسد للدراسات القرآنية تعلن نتائج مسابقة (ميثاق الرسول)

شعبة الخطابة الحسينية النسوية تنظّم مسابقة فرقية لطالبات برنامج ثمار العطاء

قسم العلاقات ينظم ورشة عن فن الإقناع والتواصل الفعّال للطلبة المنسقين

المزيد

الآخبار الصحية

تغيير بسيط في نمط التفكير قد يحدث فرقا كبيرا لصحة الدماغ ؟

لماذا ينعشنا المشروب الساخن في الطقس الحار؟

علماء يكتشفون فئة دم فريدة من نوعها في العالم !

لماذا ينصح الأطباء بزيت الزيتون يوميا؟

المزيد

الآخبار التكنلوجية

حساس الإطارات.. ما هو وعلامات تلفه وكيفية صيانته؟

ما معنى أودي Quattro؟ سر الأداء والتميز الهندسي ؟!

فصل الشاحن أم الهاتف أولا؟.. عادات بسيطة تطيل عمر البطارية

تعود للقرن الرابع قبل الميلاد.. اكتشاف بقايا "إيمت" المصرية

المزيد

مواضيع ذات صلة

Alkylation of nitroalkanes

Alkylation of nitriles

Some important considerations that affect all alkylations

Electrophilic attack on conjugated dienes

Regiospecific preparation of allylic chlorides

Nucleophilic attack on allylic compounds

Radical abstraction

Radical addition

Electrophilic attack on alkenes

Regioselectivity of intramolecular reactions

Regiocontrol by choice of route

Regioselective reactions of naphthalene