The key difference between aromatic and aliphatic aldehydes is that the aromatic aldehydes have their aldehyde functional group attached to an aromatic group whereas the aliphatic aldehydes do not have their aldehyde functional group attached to an aromatic group.
Aldehydes are organic compounds having the functional group –CHO. Therefore, it has a carbonyl center (-C=O). The general formula of an aldehyde is R-CHO in which R group can be either aromatic or aliphatic. Hence, this R group determines the reactivity of this organic molecule. Aromatic aldehydes are less reactive than aliphatic aldehydes.
CONTENTS
1. Overview and Key Difference
2. What are Aromatic Aldehydes
3. What are Aliphatic Aldehydes
4. Side by Side Comparison – Aromatic vs Aliphatic Aldehydes in Tabular Form
5. Summary
What are Aromatic Aldehydes?
Aromatic aldehydes are organic molecules having the –CHO functional group attached to an aromatic group. However, we refer to this name when there is an aromatic group somewhere in the aldehyde. Aromatic groups have a delocalized pi-electron cloud because of the conjugated pi bond system (alternating pattern of single bonds and double bonds).
Figure 01: Benzaldehyde
When the functional group directly attaches to the aromatic ring, it promotes the pi orbital overlap between the orbital of carbonyl carbon and the orbitals of the aromatic group. Which in other words, the presence of the carbonyl group attached to the aromatic ring extends the delocalization of pi-electron cloud. This redistributes the effect of electron-withdrawing nature of oxygen in –CHO group which incorporate with the aromatic ring. Therefore, the aromatic ring makes the aldehyde group less electrophilic. In other words, these molecules have resonance stabilisation.
What are Aliphatic Aldehydes?
Aliphatic aldehydes are organic compounds that have no aromatic rings attached to the aldehyde group. Moreover, these molecules do not have any aromatic ring attached to anywhere of the compound.
Figure 02: Isovalerylaldehyde
Since there are no aromatic rings, these molecules have no resonance stabilization. Therefore, these molecules have highly electrophilic –CHO groups, thus, the reactivity of the molecule is very high.
What is the Difference Between Aromatic and Aliphatic Aldehydes?
Aromatic aldehydes are organic molecules having the –CHO functional group attached to an aromatic group. Aliphatic aldehydes are organic compounds which have no aromatic rings attached to the aldehyde group. This is the main difference between aromatic and aliphatic aldehydes.
Furthermore, aromatic aldehydes have resonance stabilization. Thus, the reactivity of these molecules is very less. Moreover, they are less electrophilic. But, aliphatic aldehydes have no resonance stabilization. Therefore, the reactivity is very high. In addition, the electrophilic nature is also very high.
Summary – Aromatic vs Aliphatic Aldehydes
Aldehydes are in two types as aromatic aldehydes and aliphatic aldehydes. The key difference between aromatic and aliphatic aldehydes is that aromatic aldehydes have their aldehyde functional group attached to an aromatic group whereas aliphatic aldehydes do not have their aldehyde functional group attached to an aromatic group.
Reference:
1. “Why Are Aromatic Aldehydes Less Reactive than Aliphatic Aldehydes? | Socratic.” Socratic.org. Available here
Image Courtesy:
1.’Benzaldehyde 200’By Emeldir (talk) – Own work, (Public Domain) via Commons Wikimedia
2.’Isovalerylaldehyde’By Yikrazuul – Own work, (Public Domain) via Commons Wikimedia