AM1-type semiempirical quantum chemical calculations were carried out to explain differences in herbicidal activity between certain phenoxyacetic acid derivatives. It was found that the proper orientation and shape of the COOH group and the phenyl moiety both mutually and individually affected the observed activities. | Turk J Biol 24 (2000) 291–298 © TÜBİTAK AM1 Treatment of Some Phenoxyacetic Acid Herbicides Lemi TÜRKER Middle East Technical University, Department of Chemistry, Ankara-TURKEY Received: Abstract: AM1-type semiempirical quantum chemical calculations were carried out to explain differences in herbicidal activity between certain phenoxyacetic acid derivatives. It was found that the proper orientation and shape of the COOH group and the phenyl moiety both mutually and individually affected the observed activities. Key Words: Herbicides, phenoxyacetic acid derivatives, 2,4-D, AM1 type calculations, weed killers. Bazı Fenoksiasetik Asit Ot Öldürücülerinin AM1 İncelenmesi Özet: Bazı fenoksiasetik asit türevleri arasındaki ot giderici (herbisit) aktivite farklarını izah için AM1 tipi yarıempirik kuvantum kimyasal hesaplar yapılmışdır. Gözlenen aktiviteler üzerinde, COOH ve fenil gruplarının uygun oryantasyon ve biçimlerinin müştereken veya ayrı ayrı etkili oldukları bulunmuşdur. Anahtar Sözcükler: Herbisitler, fenoksiasetik asit türevleri, 2,4-D, AM1 tipi hesaplar, zararlı ot öldürücüler. Introduction The discovery of the phenoxyacetic acid herbicides was made during the work of Kögl et al. (1), who showed that indole-3-acetic acid (IAA, Auxin) promotes cell elongation in plants. Auxin was isolated from plants and this stimulated the search for other compounds of related structure. 1-Naphthylacetic acid was found to be active, as was 2-naphthoxyacetic acid. This created great interest in aryloxyacetic acids as potential plant growth regulators (2). In 1942, Zimmerman and Hitchcock showed that certain chlorinated phenoxyacetic acids, such as 2,4dichlorophenoxyacetic acid (2,4-D)(I, X=Y=Cl, Z=H, n=1), were more active than the natural growth hormone IAA (II), and that they were not rapidly metabolized in the plant (3). Consequently, 2,4-D could be externally applied to cause abnormal growth and the death of the plant since it is not internally regulated like
