Pyrethrins belong to a naturally occurring group of insecticides produced by the chrysanthemum daisy - VCE - SSCE Chemistry - Question 14 - 2008 - Paper 1

To determine which analytical technique would not provide useful information about the structure of pyrethrin I (C21H28O3), we need to consider the principles behind each technique:

1. Mass Spectroscopy: This technique measures the mass-to-charge ratio of ions. It can help determine the molecular weight and the structure of the compound through fragmentation patterns. Thus, it is useful.

2. Infrared Spectroscopy: This method identifies functional groups by measuring the absorption of infrared light by the compound. It provides information about chemical bonds and functional groups, making it useful in structural analysis.

3. Atomic Absorption Spectroscopy: This technique is primarily used to analyze the concentration of metal ions in a sample. Since pyrethrin I is an organic compound and does not consist of metal ions, this method will not provide relevant information regarding its structure.

4. Nuclear Magnetic Resonance Spectroscopy: NMR is excellent for providing detailed information about the structure of organic compounds, including the arrangement of atoms. It is very useful for understanding the structure of pyrethrin I.

Based on the above analysis, the answer is atomic absorption spectroscopy (C), as it is not applicable to determining the structure of organic compounds like pyrethrin I.