Organometallics and Reactions of Aldehydes & Ketones: Structure, Nomenclature, and Synthesis

Introduction to Organometallics & Carbonyl Chemistry

Overview

This study guide covers the fundamental concepts of organometallic chemistry and the reactions of aldehydes and ketones, focusing on their structure, nomenclature, and synthetic methods. These topics are essential for understanding organic reaction mechanisms and the synthesis of important functional groups in General Chemistry.

Structure and Reactivity of Carbonyl Compounds

Key Features of Carbonyl Groups

• Carbonyl Group: Consists of a carbon atom double bonded to an oxygen atom (C=O).

• Aldehyde: The carbonyl carbon is terminal (at the end of a carbon chain).

• Ketone: The carbonyl carbon is internal (within the carbon chain).

• Electronegativity: Oxygen is highly electronegative, making the carbonyl carbon partially positive and susceptible to nucleophilic attack.

• Geometry: Carbonyl carbons are sp2 hybridized, resulting in a trigonal planar structure (~120° bond angles).

• Reactivity: Less substituted carbonyls are more reactive due to reduced steric hindrance.

Example: Reactivity Trend

• Aldehydes are generally more reactive than ketones because they are less sterically hindered and have a more positive carbonyl carbon.

Nomenclature of Aldehydes and Ketones

Systematic and Common Names

• Aldehyde Naming: Replace the terminal -e of the parent alkane with -al (e.g., methanal, ethanal).

• Ketone Naming: Replace the terminal -e of the parent alkane with -one (e.g., propanone, butanone).

• Common Names: Often used for simple aldehydes and ketones (e.g., formaldehyde, acetone).

Examples

• 3-formylbenzoic acid

• 3-methylbutanal

• 2-oxocyclohexanecarboxylic acid

• butan-2-one

• formaldehyde (methanal)

• acetaldehyde (ethanal)

• acetone

• acetophenone

Aldehyde and Ketone Producing Reactions

Preparation of Aldehydes

Aldehydes can be synthesized from various precursors using specific reagents and conditions.

Starting Material	Reagent(s)	Product
1° alcohol	PCC	aldehyde
ester	[1] DIBAL-H, [2] H2O	aldehyde
acid chloride	LiAlH(OtBu)3	aldehyde
alkyne	[1] R2BH, [2] H2O2, OH-	aldehyde

Preparation of Ketones

Starting Material	Reagent(s)	Product
2° alcohol	CrO3, Na2Cr2O7, or PCC	ketone
acid chloride	[1] R2CuLi, [2] H2O	ketone
alkyne	[1] HgSO4, H2SO4	ketone
alkene	Ozonolysis (O3, Zn, H2O)	ketone and/or aldehyde

Key Points

• PCC (Pyridinium chlorochromate): Selectively oxidizes primary alcohols to aldehydes.

• DIBAL-H (Diisobutylaluminum hydride): Reduces esters to aldehydes under controlled conditions.

• LiAlH(OtBu)3: Reduces acid chlorides to aldehydes.

• Organocuprates (R2CuLi): Convert acid chlorides to ketones.

• Ozonolysis: Cleaves alkenes to form aldehydes and ketones.

Summary Table: Aldehyde and Ketone Synthesis

Transformation	Reagent	Product
Primary alcohol → Aldehyde	PCC	Aldehyde
Secondary alcohol → Ketone	CrO3, Na2Cr2O7, PCC	Ketone
Ester → Aldehyde	DIBAL-H	Aldehyde
Acid chloride → Aldehyde	LiAlH(OtBu)3	Aldehyde
Acid chloride → Ketone	R2CuLi	Ketone
Alkyne → Aldehyde	R2BH, H2O2, OH-	Aldehyde
Alkyne → Ketone	HgSO4, H2SO4	Ketone
Alkene → Aldehyde/Ketone	Ozonolysis	Aldehyde/Ketone

Important Equations

• Oxidation of primary alcohol to aldehyde: $\ce{RCH2OH + PCC -> RCHO}$

• Reduction of ester to aldehyde: $\ce{RCOOR' + DIBAL-H -> RCHO}$

• Reduction of acid chloride to aldehyde: $\ce{RCOCl + LiAlH(OtBu)3 -> RCHO}$

• Organocuprate conversion: $\ce{RCOCl + R'2CuLi -> RCOR'}$

• Ozonolysis of alkene: $\ce{RCH=CHR' + O3 -> RCHO + R'CHO}$

Conclusion

Understanding the structure, nomenclature, and synthetic methods for aldehydes and ketones is crucial for mastering organic chemistry. These functional groups serve as key intermediates in many chemical reactions and are foundational for further study in organometallic chemistry and advanced synthesis.