光譜-已解鎖_250320_144144光譜-已解鎖_250320

The difficulty is that the COOH groups deshield the

{CH}_{2}

groups, thereby decreasing the

Δ ν / J

ratio for

{CH}_{2} - CH

; the virtual coupling results in a broadened, distorted “doublet” for the

{CH}_{3}

at 300 MHz . A similarly distorted “triplet” was shown in Figure 3.52. With some experience, such distortions are tolerable. But the overlapping peaks of the

{CH}_{2} - CH - {CH}_{2}

moiety is still beyond interpretation by inspection at 300 MHz .
難點在於 COOH 基團解除了對群的

{CH}_{2}

遮罩，從而降低了的

Δ ν / J

比率;

{CH}_{2} - CH

虛擬耦合導致

{CH}_{3}

在 300 MHz 處出現加寬、扭曲的“雙峰”。一個類似的扭曲的「三元組」如圖 3.52 所示。根據一些經驗，這種扭曲是可以容忍的。但是，

{CH}_{2} - CH - {CH}_{2}

在 300 MHz 處檢查時，部分的重疊峰值仍然無法解釋。

At 600 MHz (see Figure 3.54b), the

{CH}_{3}

group is a clean doublet resulting from coupling with the CH proton, which is no longer superposed by the

{CH}_{2}

multiplets. The CH proton is coupled, quite equally, to seven neighboring protons; this means that the CH multiplet should consist of eight peaks. And in fact it does, but the eighth peak is buried under the edge of one of the

{CH}_{2}

multiplets, each of which is a doublet of doublets, somewhat distorted. As mentioned above, the protons of each

{CH}_{2}

group are diastereotopes-meaning two different chemical shifts. The protons of each

{CH}_{2}

group couple with each other (geminal coupling) and with the CH proton (vicinal coupling); the geminal coupling is larger-hence the two multiplets of doublets of doublets.
在 600 MHz 時（見圖 3.54b），該

{CH}_{3}

群是與 CH 質子耦合產生的乾淨雙峰，它不再被

{CH}_{2}

多重態疊加。CH 質子與七個相鄰質子相當相等地耦合;這意味著 CH 多重應由 8 個峰組成。事實上確實如此，但第八個峰埋在其中一個

{CH}_{2}

多重透鏡的邊緣下，每個多重透鏡都是雙峰的雙峰，有點扭曲。如上所述，每

{CH}_{2}

組的質子都是非對映位素——這意味著兩種不同的化學位移。每

{CH}_{2}

組的質子彼此耦合（雙子耦合）並與 CH 質子耦合（近鄰耦合）;雙峰耦合更大——因此是雙峰的兩個雙峰倍數。

In summary: At 300 MHz , the spectrum is not first order since the two

{CH}_{2}

groups and the CH group are severely overlapped and cannot be analyzed by inspection. At 600 MHz , they are fairly well separated and can be analyzed by inspection despite a minor overlap and some distortion. At 300 MHz , the Pople notation is

A_{2} B_{2} {CX}_{3}

, which becomes

A_{2} G_{2} {MX}_{3}

at 600 Hz . Note that there is flexibility in choosing letters that are close together and those that are more widely separated.
總結：在 300 MHz 時，頻譜不是一階的，因為兩

{CH}_{2}

組和 CH 組嚴重重疊，無法通過檢查進行分析。在 600 MHz 時，它們之間的分離相當好，儘管有輕微的重疊和一些失真，但可以通過檢查進行分析。在 300 MHz 時，Pople 符號為

A_{2} B_{2} {CX}_{3}

，在 600 Hz 處變為

A_{2} G_{2} {MX}_{3}

。請注意，可以選擇靠得很近的字母和間隔更寬的字母。

3.12 CHIRALITY 3.12 手性

The organic chemist-in particular, the natural products chemist-must always be conscious of chirality when interpreting NMR spectra. The topic was mentioned in Section 3.6. A formal definition and a brief explanation will suffice here: Chirality expresses the necessary and sufficient condition for the existence of enantiomers.*
有機化學家，尤其是天然產物化學家，在解釋 NMR 波譜時必須始終注意手性。該主題在 Section 3.6 中提到。在這裡，一個正式的定義和簡短的解釋就足夠了：手性表達了對映異構體存在的必要和充分條件。

Impeccably rigorous but possibly a bit cryptic. The following comments may help. Enantiomers are nonsuperposable mirror images. The ultimate test for a chiral molecule is thus nonsuperposability of its mirror image. If the mirror image is superposable, the molecule is achiral. The most common feature in chiral molecules is a chiral center also called a stereogenic center. A chiral molecule possesses no element of symmetry other than possibly a simple axis or axes. For examples, see Figure 3.43, structure e, and the solved Problem 7.6 (see Chapter 7). For reassurance, consider the human hand, which has no symmetry element. The left and
無可挑剔的嚴謹，但可能有點神秘。以下評論可能會有所説明。對映異構體是不可疊加的鏡像。因此，手性分子的最終測試是其鏡像的不可疊加性。如果鏡像是可疊加的，則分子是非手性的。手性分子中最常見的特徵是手性中心，也稱為立體中心。手性分子除了可能具有一個或多個簡單的軸之外，不具有任何對稱元素。有關示例，請參見圖 3.43，結構 e 和已解決的問題 7.6（參見第 7 章）。為了保證，請考慮一下沒有對稱元素的人手。左側和

right hands are nonsuperposable mirror images (i.e., enantiomers). The term “chirality” translates from Greek as “handedness.”
右手是不可疊加的鏡像（即對映異構體）。“手性”一詞從希臘語翻譯過來，意思是“慣用手”。

3.12.1 One Chiral Center, Ipsenol
3.12.1 一個手性中心，Ipsenol

The familiar carbon chiral center has four different substituents as shown in 3-hydroxybutanoic acid (compound e in Figure 3.43). This chiral center is designated

R

in accordance with the well-known priority-sequence rules; in the enantiomeric compound, the chiral center is designated

S

. Both enantiomers give the same NMR spectrum in an achiral solvent, as does the racemate. Because of the chiral center, there is no symmetry element, and the methylene protons are diastereotopes.
熟悉的碳手性中心有四個不同的取代基，如 3-羥基丁酸（圖 3.43 中的化合物 e）所示。該手性中心是根據眾所周知的優先順序序列規則指定的

R

;在對映體化合物中，手性中心被指定為

S

。兩種對映異構體在非手性溶劑中產生相同的 NMR 譜圖，外消旋體也是如此。由於手性中心，沒有對稱元素，亞甲基質子是非對映位素。

Chemical shift nonequivalence of the methyl groups of an isopropyl moiety near a chiral center is frequently observed; the effect has been measured through as many as seven bonds between the chiral center and the methyl protons. The methyl groups in the terpene alcohol, 2-methyl-6-methylen-7-octen-4-ol (ipsenol) are not chemical shift equivalent (Figure 3.55). They are diastereotopic, so a strong magnetic field is usually necessary to avoid superposition.
經常觀察到手性中心附近異丙基部分的甲基的化學位移不等效性;這種效應是通過手性中心和甲基質子之間多達七個鍵來測量的。萜烯醇中的甲基 2-甲基-6-甲基-7-辛烯-4-醇（ipsenol）不是化學位移等效物（圖 3.55）。它們是非對映位的，因此通常需要強磁場以避免疊加。

Since the nonequivalent methyl groups are each split by the vicinal CH proton, we expect to see two separate doublets. At 300 MHz , unfortunately, the pattern appears to be a classical triplet, usually an indication of a

{CH}_{3} - {CH}_{2}

moiety-impossible to reconcile with the structural formula and the integration. Higher resolution would pull apart the middle peak to show two doublets.
由於非等效甲基每個都被附近的 CH 質子分裂，我們預計會看到兩個單獨的雙峰。在 300 MHz 時，不幸的是，該模式似乎是一個經典的三元組，通常表示一個

{CH}_{3} - {CH}_{2}

部分不可能與結構公式和積分相協調。更高的解析度會拉開中間峰，顯示兩個雙峰。

To remove the coincidence of the inner peaks that caused the apparent triplet, we used the very effective technique of “titration” with deuterated benzene,* which gave convincing evidence of two doublets at

20 % C_{6} D_{6} / 80 % {CDCl}_{3}

and optimal results at about a

50 : 50

mixture (Figure 3.55). At 600 MHz , two individual doublets are seen.
為了消除導致明顯三重態的內峰的重合，我們使用了非常有效的氘代苯“滴定”技術*，這提供了令人信服的證據，證明兩個雙峰在大約一種

50 : 50

混合物下

20 % C_{6} D_{6} / 80 % {CDCl}_{3}

具有最佳結果（圖 3.55）。在 600 MHz 時，可以看到兩個單獨的雙峰。

FIGURE 3.55 2-Methyl-6-methylen-7-octen-4-ol (ipsenol) in

{CDCl}_{3}

at 300 MHz . “Titration” with

C_{6} D_{6}

. The sample was a gift from Phero Tech, Inc., Vancouver, BC, Canada.
圖 3.55 2-甲基-6-甲基-7-辛烯-4-醇（異丙烯醇），在 300 MHz .

{CDCl}_{3}

用「滴定」。

C_{6} D_{6}

該樣品是來自加拿大不列顛哥倫比亞省溫哥華市 Phero Tech， Inc. 的禮物。

Note that the chiral center accounts for the fact that the protons of each of the two aliphatic methylene groups are also diastereotopic. As a result, the rather simple structure presents a challenge in assigning the spectrum to the given structure.
請注意，手性中心解釋了兩個脂肪族亞甲基中的每一個的質子也是非對映素的事實。因此，相當簡單的結構在將頻譜分配給給定結構時提出了挑戰。

The proton integration ratios from left to right are: 1:4:1:1:1:2:1:1:6 which accounts for 18 protons in accord with the molecular formula

C_{10} H_{18} O

, but there are puzzling discrepancies. The six-proton step at

δ 0.92

in the integration represents the diastereotopic methyl protons described above, and the one-proton integration step at

δ 3.82

with several different coupling constants is a good choice for the CHOH proton (see Appendix A, Chart A.1). So far, so good. But there are four

{CH}_{2}

groups in the structure and apparently only one in the integration ratios and even this one is misleading.
質子積分比從左到右為：1：4：1：1：1：2：1：6，根據分子式

C_{10} H_{18} O

，佔 18 個質子，但存在令人費解的差異。積分中的六質子階躍 at

δ 0.92

代表上述非對映位甲基質子，

δ 3.82

而具有幾個不同耦合常數的單質子積分階躍是 CHOH 質子的不錯選擇（見附錄 A，圖 A.1）。目前為止，一切都好。但是結構中有四個

{CH}_{2}

組，而積分率顯然只有一個組，即使是這個組也具有誤導性。

It will help at this point to realize that the molecule consists of three spin systems with the “insulation” point at C-6 (see Section 3.5.2). The alkyl system consists of

H - 1, H - 2, H - 3, H - 4, H - 5

, and

H - 9

; an alkene system consists of H-7 and H-8; and another alkene system consists of

H - 10

. The alkyl system accounts for the multiplets at the right of the spectrum, and the alkenes account for the multiplets at the left side. It will also help to reiterate that the protons of an alkyl

{CH}_{2}

group will be diastereotopic in the presence of a chiral center. As will be the protons of an alkene

= {CH}_{2}

group.
在這一點上，意識到分子由三個自旋系統組成，其中“絕緣”點位於 C-6（參見第 3.5.2 節）。烷基系統由

H - 1, H - 2, H - 3, H - 4, H - 5

和

H - 9

;烯烴系統由 H-7 和 H-8 組成;另一個烯烴系統由組成。

H - 10

烷基系統占光譜右側的多重態，烯烴佔左側的多重態。這也將有助於重申烷基

{CH}_{2}

的質子在手性中心存在下將是非對映位的。烯烴

= {CH}_{2}

基團的質子也是如此。

It should now be apparent that the diastereotopic protons of each alkyl group

{CH}_{2}

group occur as a pair. One pair (

H - 3

) is at

δ 1.28

and

δ 1.42

; the other pair

(H - 5)

is at

δ 2.21

and

δ 2.48

. The two-proton multiplet at

δ 1.80

will be discussed later.
現在應該很明顯，每個烷基基

{CH}_{2}

團的非對映素質子都是成對出現的。一對（

H - 3

）位於

δ 1.28

和

δ 1.42

;另一對

(H - 5)

是 at

δ 2.21

和

δ 2.48

。雙質子多重

δ 1.80

態將在後面討論。

Furthermore, the H-5 protons are at higher frequency because they are deshielded by both the OH group and the

C = {CH}_{2}

group whereas the

H - 3

protons are deshielded only by the OH group. The H-5 protons couple geminally and each proton couples once vicinally; thus there is a doublet of doublets (first order) for each C-5 proton. The H-3 protons couple geminally and vicinally to two protons; the result for the

H - 3

protons (at 300 MHz ) is two complex multiplets. Also in favor of the first-order status for the

H - 5

protons is a larger

Δ ν

value (in Hz ) between the two

H - 5

multiplets.
此外，H-5 質子的頻率更高，因為它們被 OH 基團和

C = {CH}_{2}

基團解除遮罩，而

H - 3

質子僅被 OH 基團解除遮罩。H-5 質子在雙子上耦合，每個質子在附近偶聯一次;因此，每個 C-5 質子都有一個雙峰（一階）。H-3 質子在雙子上和附近耦合到兩個質子;

H - 3

質子（在 300 MHz 時）的結果是兩個復多重態。同樣有利於

H - 5

質子的一階狀態的是兩個

H - 5

倍數之間的較大

Δ ν

值（以 Hz 為單位）。

The mysterious multiplet at

δ 1.80

may now be identified by default as the highly coupled

H - 2

proton superposed on the OH peak, which could be confirmed by heating, by a solvent change, or by shaking the solution with

D_{2} O

to remove it (see Section 3.6.1.1). Dilution moves it to a lower frequency. The very small peak at about

δ 2.05

is an impurity.
神秘的多重

δ 1.80

態現在可以默認識別為疊加在 OH 峰上的高度耦合

H - 2

質子，這可以通過加熱、更換溶劑或搖動溶液

D_{2} O

將其去除來確認（參見第 3.6.1.1 節）。稀釋會將其移動到較低的頻率。大約

δ 2.05

非常小的峰是雜質。

Predictably the

H - 7

alkene proton is at the high frequency end of the spectrum. It couples trans (

J = 18 Hz

) and cis (

J = 10.5 Hz

) across the double bond to the

H - 8

protons to give a doublet of doublets (see Appendix F).
可以預見的是，

H - 7

烯烴質子位於光譜的高頻端。它將跨雙鍵的反式（

J = 18 Hz

）和順式（

J = 10.5 Hz

）耦合到質子上

H - 8

，得到一個雙聯體的雙峰（見附錄 F）。

The absorptions between about 1585 Hz and 1525 Hz contain the peaks from both the H-8 and H-10 protons. At the left side, there is an 18 Hz doublet representing one of the

H - 8

protons coupled trans across the double bond to

H - 7

. These doublet peaks are at 1585 Hz and 1567 Hz .
大約 1585 Hz 和 1525 Hz 之間的吸收包含來自 H-8 和 H-10 質子的峰。在左側，有一個 18 Hz 雙重態，代表通過雙鍵耦合反式的

H - 8

質子之一。

H - 7

這些雙峰峰值為 1585 Hz 和 1567 Hz。

At 1546 Hz and 1525 Hz are the two individual peaks (not a doublet) of the

H - 10

protons. The very small geminal coupling results in slight broadening; the jagged edges are evidence of some long-range coupling. Note that the height of the right-hand peak is suspicious.
在 1546 Hz 和 1525 Hz 處是

H - 10

質子的兩個單獨峰（不是雙峰）。非常小的雙齒耦合導致輕微的增寬;鋸齒狀的邊緣是一些長距離耦合的證據。請注意，右側峰值的高度是可疑的。

Having determined the trans coupling of one of the H-8 protons, we search for the corresponding doublet of the cis coupling. Unfortunately, we seem to be left with only a singlet at about 1538 Hz but quickly assume that the missing peak is buried under the suspiciously large peak at the right edge. Examination at 600 MHz of these diene spin systems clearly shows the (H-8) 10.5 Hz doublet, appropriate for the cis coupling, and justifies the above conclusions. Note the problems engendered by a chiral center.
在確定了 H-8 質子之一的反式耦合后，我們搜索順式耦合的相應雙峰。不幸的是，我們似乎只剩下一個大約 1538 Hz 的單峰，但很快就假設缺失的峰被埋在右邊緣可疑的大峰下。在 600 MHz 下對這些二烯自旋系統的檢查清楚地表明（H-8） 10.5 Hz 雙合態適用於順式耦合，並證明瞭上述結論的合理性。請注意手性中心引起的問題。

3.12.2 Two Chiral Centers
3.12.2 兩個手性中心

1,3-Dibromo-1,3-diphenylethane has a methylene group between two identical chiral centers (Figure 3.56 ). In the

1 R, 3 R

compound (one of a racemic pair),

H_{a}

and

H_{b}

are equivalent and so are

H_{c}

and

H_{d}

, because of a

C_{2}

axis. In the

1 S, 3 R

compound (a meso compound), attempted

C_{2}

rotation gives a distinguishable structure. But

H_{a}

and

H_{b}

are enantiotopes by interchange through the plane of symmetry shown perpendicular to the plane of the page.

H_{c}

and

H_{d}

, however, cannot be interchanged since they are in the plane of symmetry; they are diastereotopes.
1,3-二溴-1,3-二苯乙烷在兩個相同的手性中心之間具有亞甲基（圖 3.56）。在

1 R, 3 R

化合物（外消旋對之一）中，

H_{a}

和

H_{b}

是等價的，也是

H_{c}

和

H_{d}

，因為有一個

C_{2}

軸。在

1 S, 3 R

化合物（一種中數化合物）中，嘗試

C_{2}

旋轉會產生可區分的結構。但是

H_{a}

和

H_{b}

是對映位體通過垂直於頁面平面顯示的對稱平面交換。

H_{c}

然而

H_{d}

，由於在對稱平面上，所以不能互換;它們是非對映位素。

In the

(1 R, 3 R)

compound,

H_{a}

and

H_{b}

are not magnetic equivalent since they do not identically couple to

H_{c}

or to

H_{d}; H_{c}

and

H_{d}

also are not magnetic equivalent since they do not identically couple to

H_{a}

H_{b}

. But since the

J

values approximately average out by free rotation, the spin system is treated as

A_{2} X_{2}

and the spectrum would show two triplets. In the (

1 S, 3 R

)
在化合物中

(1 R, 3 R)

，

H_{a}

不是

H_{b}

磁性等效物，因為它們不完全相同地

H_{c}

耦合或 to

H_{d}; H_{c}

，

H_{d}

也不是磁性等價物，因為它們不完全相同地

H_{a}

耦合到或

H_{b}

。但是由於這些

J

值大約通過自由旋轉平均，因此自旋系統被視為

A_{2} X_{2}

，光譜將顯示兩個三元組。在（）

1 S, 3 R

）

(1R,3R)-1,3-Dibromo-1,3-diphenylpropane
（1R，3R）-1,3-二溴-1,3-二苯丙烷

(1S,3R)-1,3-Dibromo-1,3-diphenylpropane
（1S，3R）-1,3-二溴-1,3-二苯丙烷
FIGURE 3.56 Two isomers of 1,3-dibromo-1,3-diphenylpropane. In the

(1 R, 3 R)

-isomer,

H_{a}

and

H_{b}

are chemical-shift equivalent, as are

H_{c}

and

H_{d}

. In the (

1 S, 3 R

)-isomer,

H_{a}

and

H_{b}

are chemical-shift equivalent, but

H_{c}

and

H_{d}

are not.
圖 3.56 1,3-二溴-1,3-二苯丙烷的兩種異構體。在

(1 R, 3 R)

-isomer 中，

H_{a}

和

H_{b}

是化學位移等價物，和

H_{d}

也是

H_{c}

。在（

1 S, 3 R

）-異構體中，

H_{a}

和

H_{b}

是化學位移等價物，但

H_{c}

和

H_{d}

不是。
compound

J_{ad} = J_{bd}

and

J_{ac} = J_{bc}

; thus in this molecule,

H_{a}

and

H_{b}

are magnetic equivalent. The question of magnetic equivalence of

H_{c}

and

H_{d}

is not relevant since they are not chemical-shift equivalent. The spin system is

A B X_{2}

.
compound

J_{ad} = J_{bd}

和

J_{ac} = J_{bc}

;因此在這個分子中，

H_{a}

和

H_{b}

是磁性等效的。和

H_{d}

的

H_{c}

磁等效性問題無關緊要，因為它們不是化學位移等效的。自旋系統是

A B X_{2}

。

In the above compound, both chiral centers have the same substituents. In a compound with two chiral centers in which such is not the case, there is no symmetry element; none of the protons would be interchangeable.
在上述化合物中，兩個手性中心具有相同的取代基。在具有兩個手性中心的化合物中，如果情況並非如此，則沒有對稱元素;沒有一個質子是可以互換的。

3.13 VICINAL AND GEMINAL COUPLING
3.13 鄰接和雙叉耦合

Coupling between protons on vicinal carbon atoms depends primarily on the dihedral angle

ϕ

between the

H - C - C^{'}

and the

C - C^{'} - H^{'}

planes. This angle can be visualized by an end-on view (Newman projection) of the bond between the vicinal carbon atoms
質子在附近碳原子上的耦合主要取決於

H - C - C^{'}

和

C - C^{'} - H^{'}

平面之間的二面角

ϕ

。這個角度可以通過附近碳原子之間鍵的端接視圖（紐曼投影）來可視化

- Cahn, R.S., Ingold, C., and Prelog, V. (1966). Angew: Chem., Int. Ed. EngL., 5, 385.
  Cahn， R.S.、Ingold， C. 和 Prelog， V. （1966）。Angew： Chem.， Int. Ed. EngL.， 5， 385.
- Sanders, J.K.M., and Hunter, B.K. (1993). Modern NMR Spectroscopy, 2nd ed. Oxford: Oxford University Press, p. 289.
  Sanders， JKM 和 Hunter， B.K.（1993）。現代核磁共振波譜學，第 2 版，牛津：牛津大學出版社，第 289 頁。

3.12 CHIRALITY 3.12 手性

3.12.1 One Chiral Center, Ipsenol3.12.1 一個手性中心，Ipsenol

3.12.2 Two Chiral Centers3.12.2 兩個手性中心

3.13 VICINAL AND GEMINAL COUPLING3.13 鄰接和雙叉耦合

3.12.1 One Chiral Center, Ipsenol
3.12.1 一個手性中心，Ipsenol

3.12.2 Two Chiral Centers
3.12.2 兩個手性中心

3.13 VICINAL AND GEMINAL COUPLING
3.13 鄰接和雙叉耦合