Organic Chemistry

Introduction 483

that the unknown compound is an aldehyde; if a mirror does not form, you know that
the compound is not an aldehyde. Another example of a simple test is the Lucas test,
which distinguishes primary, secondary, and tertiary alcohols by how rapidly the test
solution turns cloudy after the addition of the Lucas reagent (Section 12.1). These
procedures were not sufficient to characterize molecules with complex structures, and
because a relatively large sample was needed to carry out all the tests, they were
impractical for the analysis of compounds that were difficult to obtain.
Today, a number of different instrumental techniques are used to identify organic
compounds. These techniques can be performed quickly on small amounts of a com-
pound and can provide much more information about the compound’s structure than
simple chemical tests can provide. We have already discussed one such technique:
ultraviolet/visible (UV/Vis) spectroscopy, which provides information about organ-
ic compounds with conjugated double bonds. In this chapter, we will look at two
more instrumental techniques: mass spectrometry and infrared (IR) spectroscopy.
Mass spectrometryallows us to determine the molecular massand the molecular
formulaof a compound, as well as certain structural featuresof the compound.
Infrared spectroscopyallows us to determine the kinds of functional groupsa com-
pound has. In the next chapter, we will look at nuclear magnetic resonance (NMR)
spectroscopy, which provides information about the carbon–hydrogen framework of
a compound. Of these instrumental techniques, mass spectrometry is the only one
that does not involve electromagnetic radiation. Thus, it is called spectrometry,
whereas the others are called spectroscopy.
We will be referring to different classes of organic compounds as we discuss the
various instrumental techniques; these classes are listed in Table 13.1. (They are also
listed inside the back cover of the book for easy reference.)

Table 13.1 Classes of Organic Compounds

CC

C C

H bonds

Alkane contains only C

and C

Alkene

Alkyne CC

RCH

O

Aldehyde

Nitrile CN

RCR

O

Ketone

RCOH

O

Carboxylic acid

RCOR

O

Ester

RCNH 2

O

Amides

RCNHR

O

Amine (secondary) R 2 NH

RCNR 2

O

Amine (tertiary) R 3 N

Amine (primary) RNH 2

Alkyl halide RX

Ether ROR

Alcohol

Aniline

ROH

X = F, Cl, Br, or I

Phenol

ArNH 2

ArOH Ar =