3,3-dimethyl-1-butene 3,3-二甲基-1-丁烯

Structure: 


IUPAC Name: 3,3-dimethyl-1-butene

Analysis: C₆H₁₂: MW = 84.16


IH NMR


The proton NMR has a singlet representing nine equivalent hydrogens (three -CH₃ groups) and two highly split multiplets in the region  5 - 6 (the alkene region). The singlet strongly suggests the presence of a tert-butyl group (-C(CH₃)₃), while the multiplets suggest a terminal alkene ABC splitting pattern.






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C13 NMR



















1³C NMR Assignments:
C-13 NMR: q-30.6; s-45.2; d-149.3; t-108.5

The ¹³C spectrum contains four peaks; a quartet at  31, a weak singlet at  45, a doublet at  149 and a triplet at  108. The quartet most likely represents a relatively simple methyl group, bonded to a carbon, and the singlet most likely represents a carbon with no hydrogens, bonded to a mildly electronegative group. The doublet and triplet are in the alkene region; the triplet is somewhat shielded, perhaps due to a steric effect in the ©-position.



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MASS SPECTRUM





Mass Spectrum Fragments: 
The mass spectrum consists of a molecular ion at 84, and a base peak at m-15 (m/e = 69) which is consistent with loss of a CH₃ group. The spectrum is consistent with a simple molecule which can lose a methyl group to form a stable radical cation.



IR




3400-3200 cm^-1: no OH peak 3100 cm^-1: sharp peak, suggesting unsaturated CH 2900 cm^-1: strong peak suggesting saturated CH 2200 cm^-1: no unsymmetrical triple bonds 1750 cm^-1: no carbonyl 1650 cm^-1: strong peak, suggesting a carbon-carbon double bond

3-methyl-2-butanone

Methyl Isopropyl Ketone

3-methyl-2-butanone


Structure: 
IUPAC Name: 3-methyl-2-butanone
Analysis: C₅H₁₀O: MW = 86.13



1H NMR




The proton NMR has a septet at  2.8 coupled to a doublet at  1.1, strongly suggesting the presence of an isopropyl group, and a singlet at  2.2 suggesting an isolated methyl group next to a mildly electronegative group (a carbonyl?).



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13C NMR
¹³C NMR Assignments: 
C-13 NMR: q-22.0; q-16.7; d-45.2; s-210.2 
The ¹³C spectrum contains four peaks; quartets at  22 and 17, a doublet at  45, and a weak singlet at  210. The quartets most likely represent relatively simple methyl groups, the doublet most likely represents a carbon bonded to a mildly electronegative group and the singlet at  210 is in the carbonyl region, most likely a ketone or aldehyde.











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MASS SPECTRUM






Mass Spectrum Fragments: 
The mass spectrum consists of a molecular ion at 86, an m-15 peak at 71, which is consistent with loss of a CH₃ group, and a base peak at m-43 (m/e = 43) which suggests the formation of an acylium ion (CH₃-CO). The spectrum is consistent with a molecule which can lose a methyl group, or can undergo fragmentation to form the acylium radical cation.





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IR


3400-3200 cm^-1: no OH peak 3100 cm^-1: no significant peak, suggesting no unsaturated CH 2900 cm^-1: strong peak suggesting saturated CH 2200 cm^-1: no unsymmetrical triple bonds 1710 cm^-1: strong carbonyl, suggesting aldehyde or ketone 1650 cm^-1: no significant peaks, suggesting no carbon-carbon double bonds






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RAMAN





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2 BUTANONE .....SPECTROSCOPY PROBLEM

Butanone, also known as methyl ethyl ketone or MEK, is an organic compound with the formula CH₃C(O)CH₂CH₃. This colorless liquid ketone has a sharp, sweet odor reminiscent of butterscotch and acetone. It is produced industrially on a large scale, and also occurs in trace amounts in nature. It is soluble in water and is commonly used as an industrial solvent

Example 

C₄H₈O
MW 72
First calculate the degree of unsaturation: the answer is 1. This means that the compound has four carbons and an oxygen, it can have a carbon-carbon double bond, a carbon-oxygen double bond - a carbonyl, or a ring.

IR Spectrum

A table of characteristic IR absorptions is available online: click on the link below. Note that this chart is also linked to in the frame to the left.
The IR spectrum for Example 1 is below. Since the degree of unsaturation indicates that the compound could have a carbonyl, let's look for that first, since carbonyl bands are strong and distinct. Carbonyls show up in the region 1760-1665, and specifically, saturated aliphatic ketone close to 1715. Sure enough, there is a band at 1718 indicating a saturated aliphatic ketone.

Think of possible structures

Now we know that the compound has a carbon-oxygen double bond, but there are still a few ways that this four-carbon molecule could be put together. Examples are below:

The second and third structures above are saturated aliphatic aldehydes, which show up at 1740-1720. While in the above IR spectrum the band at 1715 might be close to the range of saturated aliphatic aldehydes, an aldehyde would also show a distinct band for H-C=O stretch in the region 2830-2695, so it is not likely that it is one of these structures. That leaves the first compound, which is 2-butanone.

Proton NMR Spectrum

A table of characteristic NMR shifts is available online: click on the link below. Note that this chart is also linked to in the frame to the left.

• Before you look at the NMR spectrum, think about what the spectrum of 2-butanone should look like. There are three different types of protons:

The 3 protons in green will be a singlet and show up from 2-2.7 ppm. The 2 protons in blue will be split to a quartet by the protons in red; they will show up from 2-2.7 ppm. They will be further downfield (have a higher ppm value) than the protons in green because they are shielded both by the carbonyl and by the red methyl group. The 3 red protons are the farthest from the carbonyl and are split into a triplet by the blue protons. Let's look at the NMR and see if this is what we see.

Sure enough, here is how they correlate with the structure:

Note the pattern of the ethyl group -CH₂CH₃ in the above NMR spectrum. Whenever you suspect an ethyl group in a molecule, look for a quartet of 3 protons and a triplet of 2 protons, with the methylene (-CH₂-) group further downfield than the methyl group (-CH₃).

Summary

Example 1 is 2-butanone:

COSY