Infrared Spectroscopy of Organic Compounds: A Comprehensive Guide

Infrared Spectra of Alkanes

Alkanes, being saturated hydrocarbons, only contain Carbon-Carbon (C-C) and carbon-hydrogen single bonds. Their IR spectra are relatively simple due to the absence of strong functional groups.

C-H Stretching

The most prominent peaks in an alkane's IR spectrum are due to C-H stretching vibrations. These sharp, strong bands typically appear in the range of 2850-2960 cm^-1. The exact wavenumber can vary slightly depending on the specific alkane and its branching.

Infrared Spectra of Alkenes

Alkenes contain at least one carbon-carbon double bond (C=C), along with C-H bonds. The presence of the double bond introduces distinct features in their IR spectra compared to alkanes.

C=C Stretching

The stretching vibration of the C=C double bond usually gives rise to a moderate band in the region 1680-1840 cm^-1.

C-H Stretching

Stretching vibrations of the C-H bond are of higher frequency (higher wavenumber) than those of the C-C-H bond in alkanes. The strongest bands in the spectra of alkenes are those attributed to the carbon-hydrogen bonding of the -C-H group. These bands are in the region 1000-650 cm^-1 (this overlaps the fingerprint region).

Infrared Spectra of Ketones

The carbonyl stretching vibration band (C=O) of saturated aliphatic ketones appears at 1715 cm^-1.

Conjugation of the carbonyl group with carbon-carbon double bonds or phenyl groups, as in alpha, beta, and benzaldehyde, shifts this band to lower wavenumbers (1685-1666 cm^-1).

Infrared Spectra of Aldehydes

The carbonyl stretch of saturated aliphatic aldehydes appears from 1740-1720 cm^-1. As in ketones, if the carbon adjacent to the aldehyde group is unsaturated, this vibration is shifted to lower wavenumbers.

Another useful diagnostic band for aldehydes is the O=C-H stretch. This band generally appears as one or two bands of moderate intensity in the region 2830-2695 cm^-1. Since the band near 2830 cm^-1 is usually indistinguishable from other C-H stretching vibrations, the presence of a moderate band is more likely to be helpful in determining whether a compound is an aldehyde or not.

Infrared Spectra of Carboxylic Acids

C-O Stretch

The most prominent peak in the spectrum appears as a broad and strong band in the range of 1760-1690 cm^-1. The broadness is due to the presence of hydrogen bonding between carboxylic acid molecules.

O-H Stretch

This peak appears as a broad band in the region of 3300-2500 cm^-1, centered around 3000 cm^-1. It often overlaps with the C-H stretching bands.

C-O Stretch

It appears in the range of 1320-1210 cm^-1.

O-H Band

It appears in the region of 1440-1395 cm^-1 and 950-910 cm^-1.

Magnesium Ions (Mg²⁺)

Energy Production

ATP Formation and Stability

Mg²⁺ is essential for the synthesis and stabilization of adenosine triphosphate (ATP), the primary energy carrier in cells. It binds to ATP and is required for the activation of enzymes that utilize ATP for energy transfer.

Enzyme Activation

Many enzymes involved in glycolysis, the Krebs cycle, and the electron transport chain require Mg²⁺ as a cofactor. These enzymes are critical for the conversion of glucose and other nutrients into usable energy.

Chlorophyll

Central Atom in Chlorophyll

Mg²⁺ is the central atom in the chlorophyll molecule, which is crucial for photosynthesis. It helps in capturing light energy and converting it into chemical energy.

Light Absorption

The presence of Mg²⁺ in chlorophyll aids in the efficient absorption of light, particularly in the blue and red wavelengths, which are vital for the photosynthetic process.

Calcium Ions (Ca²⁺)

Blood Clotting

Activation of Clotting Factors

Ca²⁺ is essential for the activation of several clotting factors in the coagulation cascade. It acts as a cofactor for enzymes like prothrombinase and is necessary for the conversion of prothrombin to thrombin.

Platelet Aggregation

Ca²⁺ facilitates the aggregation of platelets at the site of a blood vessel injury, which is crucial for forming the initial platelet plug.

Structural Role

Bone and Teeth Formation

Ca²⁺ is a primary component of hydroxyapatite, the mineral that gives bones and teeth their hardness and strength. It provides the structural rigidity necessary for skeletal support and protection.

Cell Membrane Stability

Ca²⁺ helps stabilize cell membranes by interacting with phospholipids, maintaining the integrity and functionality of cellular structures.