default_background
✕

Find the best tutors and institutes for Class 12 Tuition

Find Best Class 12 Tuition

Please select a Category.

Please select a Locality.

No matching category found.

No matching Locality found.

Q8.16(iii):
Describe the following: (iii) Cross aldol condensation

Solution :

Definition and Theoretical Foundation

Cross Aldol Condensation is a chemical reaction involving two different carbonyl compounds (aldehydes or ketones), at least one of which must possess $\alpha$-hydrogen atoms. In the presence of a dilute alkali (base) catalyst, these compounds undergo nucleophilic addition to form a mixture of four distinct $\beta$-hydroxy aldehyde or $\beta$-hydroxy ketone products (aldols), which can subsequently undergo dehydration to form $\alpha,\beta$-unsaturated carbonyl compounds.

Mechanism and Sequential Analysis

Consider the reaction between Ethanal ($CH_3CHO$) and Propanal ($CH_3CH_2CHO$).

  • Step 1: Generation of Enolate Ions: The base ($OH^-$) abstracts an $\alpha$-proton from both aldehydes, generating two distinct enolate ions:
    $- CH_3CHO + OH^- \rightleftharpoons ^-CH_2CHO + H_2O$
    $- CH_3CH_2CHO + OH^- \rightleftharpoons CH_3\bar{C}HCHO + H_2O$
  • Step 2: Nucleophilic Attack (Cross Addition): Each enolate can attack the carbonyl carbon of either the original or the partner aldehyde. [Per the mechanism of Nucleophilic Addition to Carbonyls].

Product Distribution Matrix

Electrophile Nucleophile Product Type
Ethanal Ethanal (Self) 3-hydroxybutanal
Propanal Propanal (Self) 3-hydroxy-2-methylpentanal
Propanal Ethanal (Cross) 3-hydroxypentanal
Ethanal Propanal (Cross) 3-hydroxy-2-methylbutanal

Synthetic Utility and Limitations

The primary challenge in cross-aldol condensation is the formation of a complex mixture of four products. In industrial synthesis, this method is only considered "useful" if:

  1. One of the carbonyl compounds lacks an $\alpha$-hydrogen (e.g., Benzaldehyde or Formaldehyde), which cannot form an enolate.
  2. The reaction is performed under controlled thermodynamic conditions to favor the formation of the cross-product over self-condensation products.

Visual Representation of Cross Aldol Condensation

R-CH₂CHO + R'-CHO Dil. NaOH R-CH(OH)-CH(R'')-CHO (Alpha-hydrogen present) (No Alpha-H preferred)

Final Solution: Cross aldol condensation is a versatile organic synthesis method for forming C-C bonds between two different carbonyl species; however, it typically results in a mixture of four products unless specific substrate constraints (such as the absence of $\alpha$-hydrogens in one component) are strictly maintained.


More Questions from Class 12 Chemistry Aldehydes Exercises


CBSE Solutions for Class 12 Chemistry Aldehydes


Chapters in CBSE - Class 12 Chemistry


Top Tutors who teach Aldehydes

Sagar Chawla Class 12 Tuition trainer in Delhi
(61)
Top Tutor
locationImg Ashok Nagar, Delhi
experience 20 yrs of Exp students 7 students
greenClock 105 hrs of classes completed
rsIcon 750 per hour
MBA(F) with CFA
Online Classes Online Classes
homeTutions Student's Home

I am teacher with over experience of 20 years. Provides complete notes and assignment. And make subject more understanding and easy.

Advithya Bhardwaj

I’ve had a great experience learning under my Accounts tuition teacher. Their way of explaining concepts is clear, practical, and easy to understand, even for tough topics like journal entries, ledgers, and financial statements. They are patient, punctual, and always open to doubts—no matter how many times I ask. Thanks to their guidance, I’ve not only improved my grades but also developed a genuine interest in the subject. Their real-world examples make learning more engaging and help me understand the application of concepts beyond the textbook.

Skills: Accounts , Commerce and more
Also teaches: BBA Tuition, MBA Tuition and more

(44)
Top Tutor
locationImg HSR Layout 1st Sector, Bangalore
experience 11 yrs of Exp students 25 students
greenClock 2027 hrs of classes completed
rsIcon 400 per hour
Magic maths class for students
homeTutions Student's Home

I am a B.TECH. graduate from computer science.I am completely dedicated in teaching .I have experience of 10 years in teaching field. In that 10 years, I have taught 180 students(1 on 1)as a tutor.I have experience of teaching all types of boards like (CBSE,ICSE,IGCSE, ISC,STATE BOARD,IB) .My specialisation is in mathematics subject.I teach mathematics from 7th grade to 12th grade.I keep patience while teaching to the students,I try my best to clear the concepts regarding that chapter either in maths.Student can ask their doubts many times until their concepts is not clear.I have given good results to the students and also generated confidence in them specially in mathematics. I am the best for teaching maths subject. I first try to understand the student ( weakness and strength) and then I plan how to make any student best in math. I teach with full dedication and create interest for maths subject in my students. Thanks.

Akshith Sitaram

I wanted to express my gratitude for your exceptional guidance in math tuition. Your teaching style is not only informative but also engaging, making complex concepts seem much simpler. Your patience and willingness to go the extra mile to ensure I understand each topic are truly commendable. Thanks to your support, my confidence in math has soared, and my grades have improved significantly. Your dedication to your students' success is inspiring. I'm truly fortunate to have you as my math tutor, and I look forward to continuing to learn from you. Thank you for making math enjoyable!

Skills: Mathematics
Also teaches: BTech Tuition, BCom Tuition and more

Anwar A. Class 12 Tuition trainer in Bangalore
(20)
Top Tutor
locationImg Yamare Village, Bangalore
experience 8 yrs of Exp students 1 student
greenClock 8 hrs of classes completed
rsIcon 1500 per hour
Helping Students Achieve A & 7+ in IB/IGCSE/ICSE/CBSE | 10+ Years Coaching Experience
homeTutions Student's Home
regularClasses Tutor's home

Hello! I’m Anwar, a certified mathematics tutor with over 10 years of experience helping students excel at every stage, from Primary, Middle School to High School and University level. My passion is to make math clear, engaging, and enjoyable for learners worldwide. I specialize in teaching Maths to students from Grade 8 to Grade 12 across multiple curricula including IGCSE/Cambridge, IB (MYP), GCSE, CBSE and ICSE. I focus on concept clarity and exam-oriented preparation, helping students understand not just how to solve questions, but how to approach them logically. My teaching approach is highly interactive and student-centric. Each session begins with clear explanation of concepts, followed by strategies to decode questions and step-by-step solving methods. Students actively participate during the class and solve questions along with me, which allows me to check their understanding in real time. Once the concepts are tested, students solve questions independently while I closely monitor their working and provide instant feedback wherever required. This method helps students strengthen accuracy, speed and confidence, and is especially effective for students who feel weak or anxious in Maths and Science. I offer one-to-one personalized tutoring with a minimum class duration of one hour, ensuring complete attention and customized learning for every student.

Skills: Mathematics
Also teaches: Class 9 Tuition, Class 10 Tuition and more

(13)
Top Tutor
locationImg KR Puram, Bangalore
experience 8 yrs of Exp students 2 students
greenClock 31 hrs of classes completed
rsIcon 500 per hour
Science HOD with 8 years of experience of teaching physics to grade X,XI & XII
Online Classes Online Classes

I am a physics teacher handling X,XI,XII grades, having 8 years experience as Science HOD in a cbse School. I have a degree in BE ( electronics and telecommunications).With my best efforts, support, patience ,commitment I unlock my students potential.Concepts are presented in a clear, simple and direct manner. Consistently my class result is 100% with good subject average. Expanding pupils horizons is my accomplishment.

Skills: Physics

(28)
Top Tutor
locationImg Chembur West, Mumbai
experience 17 yrs of Exp students 14 students
greenClock 273 hrs of classes completed
rsIcon 750 per hour
An Experienced chemistry partner of you of your journey of 11 and 12
Online Classes Online Classes
regularClasses Tutor's home

I teach class11 and 12 chemistry CBSE board. I also take classes for competitive exams like NEET,JEE,PUC,etc.

Srinithya M

Pragya maam is an excellent teacher. She has vast knowledge of the subject. Her teaching methods makes the subject easy to learn and understand. She's very patient and friendly. My interest in chemistry has increased ever since I started classes from Pragya maam. I scored 98 in grade 12th boards in Chemistry. All thanks to her.

Skills: Chemistry
Also teaches: Class 11 Tuition

Other Subjects in CBSE - Class 12

Worksheet Icon

Download free CBSE - Class 12 Chemistry Aldehydes Exercises worksheets

Download Now

Find Best Class 12 Tuition ?

Find Now »