Isopentyl Acetate (Banana Oil)- IR Spectrum
I need help in assigning the following IR peaks: alkane C–H stretch, C=O stretch, alkane CH2 bend and C–O stretch
The Correct Answer and Explanation is :
The infrared (IR) spectrum of isopentyl acetate (also known as banana oil) shows several characteristic peaks that can be assigned to functional groups present in the compound. Below is an analysis of the specific peaks you asked about:
- Alkane C–H Stretch (around 2800–3000 cm⁻¹):
- The C–H stretch of alkanes typically appears in the 2800–3000 cm⁻¹ region. In isopentyl acetate, you would observe strong absorptions in this region due to the stretching of the C–H bonds in the alkyl chain (from the isopentyl group). This corresponds to the saturated carbon-hydrogen bonds in the molecule.
- C=O Stretch (around 1725 cm⁻¹):
- The C=O stretch of esters (like the one in isopentyl acetate) appears around 1725 cm⁻¹. This is a strong and sharp peak, typical for carbonyl groups in esters. The ester functional group is responsible for the characteristic fruity smell of banana oil. The sharpness and intensity of this peak are indicative of the C=O bond in a conjugated ester.
- Alkane CH2 Bend (around 1450 cm⁻¹):
- The CH2 bending vibration (often called the “methylene bend”) appears around 1450 cm⁻¹. This bending mode is typical for alkyl groups, where the C–H bonds in the methylene (–CH2) groups of the alkyl chain undergo deformation, causing a peak to appear in this region. It is often accompanied by the CH3 bending peak around 1375 cm⁻¹, although the methylene bending dominates at 1450 cm⁻¹.
- C–O Stretch (around 1000–1300 cm⁻¹):
- The C–O stretching vibration typically appears in the 1000–1300 cm⁻¹ region. This is a characteristic peak for esters and alcohols, and in isopentyl acetate, the ester C–O bond will show a stretch around 1050–1300 cm⁻¹, depending on the exact molecular environment. The C–O bond in esters typically appears in the lower end of this region (around 1050–1150 cm⁻¹).
Summary:
- Alkane C–H stretch: 2800–3000 cm⁻¹
- C=O stretch: 1725 cm⁻¹ (strong, sharp)
- Alkane CH2 bend: 1450 cm⁻¹
- C–O stretch: 1050–1300 cm⁻¹
These peaks are typical for isopentyl acetate, and they provide valuable information for identifying functional groups within the molecule.