Final answer:
IR spectra for alkynes show characteristic peaks at 2100-2250 cm⁻¹ for the triple bond and about 3300 cm⁻¹ for terminal alkynes. The peak at 1642 cm⁻¹ for 1-octene indicates an alkene C=C stretch. IR spectroscopy is used to identify functional groups and the fingerprint region (400-1400 cm⁻¹) helps in molecule identification.
Step-by-step explanation:
To describe the IR spectrum for alkyne peaks, we look at the characteristic IR absorbance peaks that alkenes and alkynes exhibit because of their unique bond structure. For alkynes, these peaks are usually found in the range of 2100-2250 cm¹, which is indicative of the stretching of the carbon-carbon triple bond. In addition, terminal alkynes can be identified by their absorbance at about 3300 cm⁻¹, which is due to the C-H bond stretching between the sp-hybridized carbon and the terminal hydrogen.
The IR spectrum for alkenes, such as 1-octene, shows the characteristic peak for the C=C double bond stretch at 1642 cm⁻¹ and a C-H stretch at about 3079 cm⁻¹. In contrast to the carbon-carbon triple bond of alkynes which are less polar and absorb weakly, the C=O bond in carbonyl compounds is very polar and absorbs very strongly, typically in the range of 1650-1750 cm²¹, with a particularly strong peak at 1716 cm⁻¹ for ketones. Understanding these characteristic peaks helps in identifying specific functional groups in a molecule using IR spectroscopy.
One important aspect of IR spectra is the 'fingerprint region' (400-1400 cm⁻¹), which contains a unique pattern of absorbance peaks for every molecule. Although it's difficult to identify specific functional groups in the fingerprint region, this region can be used to compare unknown samples to known standards for molecule identification.