The nuclear magnetic resonance (NMR) characteristics of 4-fluorocinnamic acid (4-fluorocinnamic acid) must be investigated in its molecular structure and chemical environment. For 4-fluorocinnamic acid, its molecular structure contains fluorine atoms, benzene ring and cinnamic acid.

In the NMR analysis, in the hydrogen spectrum, the hydrogen on the benzene ring shows different chemical shifts due to the difference in the chemical environment. The chemical shifts of adjacent, inter and para-hydrogen are different due to the electronegativity and conjugation effect of fluorine atoms. The existence of fluorine atoms makes the ortho-hydrogen subject to the de-shielding effect, and the chemical shifts move to the low field.

In terms of carbon spectra, the chemical shifts of benzene cyclic carbon and double-bonded carbon are also uniquely characterized by the action of fluorine atoms and conjugated systems. The electron cloud density of double-bonded carbon is reflected in the chemical shift value, which can help to analyze the molecular structure and electron cloud distribution.

In addition, the coupling constant is also key. The coupling between hydrogen-hydrogen and hydrogen-fluorine in the molecule of 4-fluorocinnamic acid forms a specific coupling cracking pattern in the spectrum. The magnitude of the hydrogen-fluorine coupling constant reveals the spatial relationship between the two, providing important clues for determining the three-dimensional structure of the molecule.

To accurately grasp the NMR properties of 4-fluorocinnamic acid, it is necessary to comprehensively consider many factors such as chemical shifts and coupling constants to clarify the relationship between molecular structure and chemical environment. This is of great significance in the fields of organic chemistry research and drug analysis.