CHE 231 Naming Cycloalkanes and 13C NMR AQ24

Cycloalkane

A saturated hydrocarbon ring consisting only of carbon and hydrogen atoms with single bonds between the carbon atoms.

Substituted Cycloalkane

A cycloalkane with one or more alkyl or other substituent groups attached to the ring.

Unsubstituted Cycloalkane

A cycloalkane without any substituent groups attached.

Prefix in Cycloalkane Naming

The prefix “cyclo” is added before the name of the alkane to indicate the presence of a ring structure.

Alkyl Substituent

A substituent derived from an alkane by removing one hydrogen atom. Common examples are methyl (-CH3), ethyl (-C2H5), etc.

Rule for Monosubstituted Cycloalkanes

If the cycloalkane has a single substituent, numbering is unnecessary. The substituent is named followed by the cycloalkane name.

Rule for Disubstituted Cycloalkanes

Number the ring starting from the substituent that gives the lowest numbers to the substituents and name them alphabetically.

Rule for Polysubstituted Cycloalkanes

Number the ring to give the lowest possible numbers to the substituents, regardless of alphabetical order.

1,3-dimethylcyclohexane

A disubstituted cycloalkane where two methyl groups are attached to carbons 1 and 3 of a cyclohexane ring.

Cis-Trans Isomerism

A form of stereoisomerism where two substituents on a cycloalkane are either on the same face (cis) or opposite faces (trans) of the ring.

Cis Isomer

In cycloalkanes, both substituents are on the same side of the ring plane.

Trans Isomer

In cycloalkanes, the substituents are on opposite sides of the ring plane.

Stereoisomer

Compounds with the same molecular formula and connectivity but different spatial arrangements of atoms.

Nuclear Magnetic Resonance (NMR)

A spectroscopic technique used to observe local magnetic fields around atomic nuclei, specifically carbon-13 in 13C NMR.

Isotopic Abundance

The relative amount of each different isotope of an element in a sample. For carbon, 12C makes up 98.9%, while 13C makes up 1.1%.

Spin States (+1/2 and -1/2)

The two possible magnetic alignments of nuclei in a magnetic field, referred to as "spin-up" and "spin-down."

Chemical Shift (δ)

The position of an NMR signal relative to a reference compound (usually TMS) and expressed in parts per million (ppm).

Tetramethylsilane (TMS)

A reference compound used in NMR spectroscopy, set at 0.00 ppm for calibration purposes.

Local Chemical Environment

The electronic and magnetic surroundings of a nucleus in a molecule that affect its chemical shift in NMR spectroscopy.

Shielded Proton

A proton surrounded by electron density, reducing the effect of the external magnetic field and resulting in a lower chemical shift (upfield).

Deshielded Proton

A proton with less electron density, experiencing a stronger external magnetic field and resulting in a higher chemical shift (downfield).

Inductive Effect

The transmission of electron density through sigma bonds in a molecule, which can influence NMR chemical shifts of neighboring atoms.

Alkyl Carbon Chemical Shift

Alkyl carbons typically have chemical shifts between 0-40 ppm in a 13C NMR spectrum.

Carbonyl Carbon Chemical Shift

Carbonyl carbons (C=O) typically show up between 160-220 ppm in a 13C NMR spectrum.

Alkenes Chemical Shift

Alkenes typically have chemical shifts in the range of 110-150 ppm.

Alcohol, Amine, and Alkyl Halide Chemical Shift

Alcohols (50-90 ppm), amines (40-80 ppm), and alkyl halides can be detected in this range in a 13C NMR spectrum.

Arene Chemical Shift

Arene (aromatic ring) carbons typically appear between 110-140 ppm in a 13C NMR spectrum.

Relationship Between Peak Intensity and Hydrogen Atoms

In 13C NMR, carbons with more attached hydrogens generally give more intense peaks.

Deshielding Effect of Heteroatoms

Heteroatoms (such as oxygen, nitrogen, and halogens) cause deshielding of nearby carbons, shifting their peaks downfield in the spectrum.

Number of Unique Car